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Last update: 29 November 1998
This document contains basic descriptions of the purpose of some possible science instruments on a spacecraft. In addition, a detailed description of each instrument from Basics of Space Flight by the Jet Propulsion Laboratory, from Chapter 12. Typical Science Instruments is included. I have taken liberty in devising parameters for these instruments for the mission.
The mission may entail a fast flyby of the target planetary system, or it may involve placing the spacecraft into orbit around the planet. Missions using landers and/or rovers require an orbital platform. Note that once you commit to a planet, there will not be enough fuel in the delivery vehicle to redirect to another! You get one shot, unless you plan for a gravity-assisted rendevous with a second target. (In this case, discuss this with the Mission Coordinator (me).
Purpose: To carry instrument suite through target planetary system at high speed. Does allow dropping of atmospheric and/or hard impact probes. Cheaper with more weight allowance than orbiter.
Detailed description: This is the most cost and weight-effective way to get a close-up view of a planet and its environment, at the expense of a short in-system duration. A hyperbolic trajectory carries the spacecraft through the system on a pre-determined path. If powerful imaging systems are started early enough (1 month before encounter) then the course can be adjusted to fly-by one of the satellites, and possibly two, of the planet. Note that this requires that the spacecraft include sufficient power for last at least that long (once powered-up, the spacecraft must remain on until powered down finally). On peri-planetary passage, an atmospheric or hard-landing probe may be dropped.
Purpose: Places science payload in orbit around planet. Gives maximum duration for experiments. An orbiter is necessary to deliver a soft lander and/or planetary rover, though it may also drop atmospheric and/or hard impact probes.
Detailed description: The orbiter is used for missions needing to spend extended time in a specific planetary system, and to drop soft landers to the planets surface. The Magellan Venus radar mapper, the Galileo mission currently in orbita around Jupiter, and the planned Cassini mission to Saturn are examples of orbiters. The Viking missions to Mars contained both orbiter and lander components. You may use the Galileo and Viking missions as guidelines for planning an orbiter mission. For example, the moons in a system can be targeted for fly-bys at a rate of 1 every 2 months of in-orbit duration (the time needed to arrange an suitable orbit). Of course, this means that sufficient power will be required to run the mission for a long time.
Direct-sensing instruments interact with phenomena in their immediate vicinity, and register characteristics of them. The Heavy Ion Counter on Galileo uses direct sensing; it registers the characteristics of ions in the spacecraft's vicinity which enter the instrument. It does not attempt to form any image of the ions' source.
Purpose: counts how much charge high-energy (usually at least 20,000 electron Volts (20keV)) particles have and how many particles it encounters. Used to measure radiation belts around planets. Manned spacecraft must avoid radiation belts. Radiation in these belts will kill people quickly, even if they are inside a spacecraft. Unmanned craft are also affected by these radiation belts and being in them limit their lifespans. In addition, scientists do not know how magnetic fields of planets interact with particles to be able charge them at such high energies.
Detailed description: High-energy Particle Detector instruments measure the energy spectra of trapped energetic electrons, and the energy and composition of atomic nuclei. They may employ several independent solid-state-detector telescopes. The Cosmic Ray instrument on Voyager measures the presence and angular distribution of electrons of 3-110 Million electron Volts (MeV) and nuclei 1-500 Million electron Volts (MeV) from hydrogen to iron. The Energetic Particle Detector on Galileo is sensitive to the same nuclei with energies from 20,000 electron Volts to 10 million electron Volts.
Purpose: Detects low-energy particles by assuming plasma has a certain shape and then computes measurements based on that. However, many plasmas do not have that shape.
Detailed description: Plasma detectors serve the low-end of particle energies. They measure the density, composition, temperature, velocity and three-dimensional distribution of plasmas, which are soups of positive ions and electrons, that exist in interplanetary regions and within planetary magnetospheres. Plasma detectors are sensitive to solar and planetary plasmas, and they observe the solar wind and its interaction with a planetary system.
Purpose: Tells about evolution of solar systems. One stage of solar system formation is the production of dust. A theory of solar system evolution is that this dust then clumps together to form asteroids, then planets. Studying the dust's charge tells whether the dust will avoid each other (like charged) or if it can clump together. Shows how plasma has or is affecting the dust by the dust's distribution in a magnetosphere.
Detailed description: Some spacecraft carry a dust detector which measures the velocity, mass, charge, flight direction and number of dust particles striking the instrument. Galileo's instrument can register up to 100 particles per second and is sensitive to particle masses of between 10 and 10 g. Also good if you are scouting out a comet or in an asteroid belt region, as long as you don't hit a big one!
Purpose: Shows changes in magnetic fields around planets over time. Shows composition of objects - if it has a magnetic field, it must have magnetic materials (e.g. sand would not have a magnetic field.) and some sort of dynamo mechanism to generate and maintain the field. Composition tells us how the object might have been formed.
Detailed description: Magnetometers are direct-sensing instruments which detect and measure the interplanetary and solar magnetic fields in the vicinity of the spacecraft. They typically detect the strength of magnetic fields in three planes. As a magnetometer sweeps an arc through a magnetic field when the spacecraft rotates, an electrical signature is produced proportional to the strength and structure of the field.
Purpose: Scientists do not know how extremely high-energy particles are formed. They think plasma waves may be responsible, and study them to understand the astrophysics of them. Shows the low-frequency plasma waves.
Detailed description: Plasma wave detectors typically measure the electrostatic and electromagnetic components of local plasma waves in three dimensions. Plasma wave data provides key information on phenomena related to the interaction of plasma and particles that control the dynamics of a magnetosphere. The instrument functions like a radio receiver sensitive to the wave lengths of plasma in the solar wind, from about 10 Hz to about 60 kHz. When within a planet's magnetosphere, it can be used to detect atmospheric lightning, and events when dust and ring particles strike the spacecraft. Voyager's Plasma Wave data has been used to produce digital sound recordings of the particle bombardment the spacecraft experienced as it passed through the ring planes of the outer planets.
Purpose: Determine local temperature, pressure, and wind velocity of environment. Pressure and wind measurements only work in atmospheres above 10^-4 bar.
Detailed description: a simple thermometer, pressure sensor, and wind velocity detector in a durable package. Very useful for finding the conditions on the ground near a lander!
Purpose: Determine atmospheric composition.
Detailed description: Mass spectrometers and some other gas analysis experiments bundled together to determine the atmospheric composition locally. When on an atmospheric probe, can determine composition as the probe descends. Also works on lander.
Purpose: Measure tectonic activity on a planet. Works only on a stable platform such as a lander.
Detailed description: pretty much the same as the ones deployed on the Moon by Surveyor and the Apollo missions. Can also be found all over L.A. - you'll know what I mean if you've lived there. Motion sensors register small (or not so small) movements of the spacecraft. Probably will be useless in high-wind environments.
Purpose: A reinforced and shielded probe designed to dig deep into the planets surface and determine the composition and temperature. Built for a hard impact probe.
Detailed description: Heavy shielding permits probe to dig into ground after surviving impact. Can burrow 10 meters or more into surface. Gives rough idea of composition below top layer.
Purpose: A mechanical arm to reach out from the lander and scoop up nearby soil samples. Of course, this requires a lander or rover.
Detailed description: Similar to the digging devices deployed by the Viking mission. If desired, could be modified to do other remote manipulation tasks, such as pick up objects (a claw), or shoot little darts at the aliens (just kidding).
Purpose: Runs a soil sample through a variety of experiments to determine the chemical and mineral composition as well as grain size distributions. Naturally, this requires a soil scoop to obtain the sample.
Detailed description: Basically a little chemistry set, chromatography, and mass spectrometer. A standard for a geology oriented mission. Can also look for organic or life-indicating compounds in the soil.
Purpose: Detect chemical changes in reaction chamber due to metabolism of nutrients or atmosphere. Requires Soil Scoop.
Detailed description: A suite of experiments designed to detect changes caused by metabolism by simple life forms (eg. bacteria). A combination of gas-exchange, labeled-release and pyrolytic-release experiments. Essentially the same as those used on the Martian Viking landers.
Remote-sensing instruments record characteristics of objects at a distance, sometimes forming an image by gathering, focusing, and recording reflected light from the sun, or reflected radar waves which were emitted by the spacecraft itself. When an instrument provides the illumination, as does radar, it is referred to as an active remote sensing instrument. If the illumination is not provided by the instrument, as in the case of cameras observing planets in sunlight, it is passive remote sensing.
Purpose: Same purpose as a plasma wave detector, but it's remote sensing. Shows the high-frequency plasma waves.
Purpose: Centimeter and Millimeter wavelength radio telescope for mapping planetary atmospheres. Can also detect dust and cometary belts.
Detailed description: A planetary radio astronomy instrument measures radio signals emitted by a target such as a Jovian planet. The instrument on Voyager is sensitive to signals between about 1 kHz and 40 MHz, and uses a dipole antenna 10 m long, which it shares with the plasma wave instrument. The planetary radio astronomy instrument detected emissions from the heliopause in 1993. Ulysses carries a similar instrument. These correspond to the low-frequency radio telescope described in the table. With only a small (~1 meter) antenna, these telescopes have poor resolution and sensitivity. The high-frequency version operates from 1 GHz (10^9 Hz) to 130 GHz, which encompasses several molecular transitions from water, ammonia masers, oxygen, and carbon monoxide. Limited (arcminute to degree) resolution is permitted, with moderate sensitivity. Who knows, maybe you will pick up radio stations from any ETs too!
General Purpose: Shows shape, surface morphology, and color of object. Shape tells origin of the object. Surface morphology tells about surface processes that have occurred/are occurring like impacts. Color shows that the different rock types. Younger rock types are on top of older. Tells how it got there, where it came from.
Note that the Filter Wheel addition is needed to make color images (except for the Planetary Camera, which already includes color capability).
Detectors have a given format, in pixels (eg. 128 x 128). Optics, focal-length in particular, may be chosen to give a desired magnification (pixel size in arc-seconds). Keep in mind the resolution limit (wavelength/diameter in radians) for a given telescope size, and that small aperture optics used at high magnifications will have poor sensitivity.
Purpose: A light, inexpensive version of the low-resolution imager
designed for guidance and rough imaging for probes, landers, and rovers.
Typically chosen to have a 7 degree field of view (similar to binoculars).
Image format: 64 x 64 pixels.
Primary lens diameter: 50mm.
Purpose: A relatively
light and inexpensive CCD imaging detector for spacecraft or entry vehicle
use. Usually set up to have a moderate (10 degree or so) field of view, and
will allow a rough determination of the surroundings and gross composition.
Will give only a low-quality image of a planet from orbit or flyby.
Image format: 128 x 128 pixels.
Primary lens diameter: 75mm.
Similar to the low resolution imager, but with an increased number of
pixels and a narrower field of view. Intended to provide images suitable for
identifications of surroundings, composition. May be used for planetary
imaging.
Image format: 256 x 256 pixels.
Primary lens diameter: 100mm.
Purpose: Shows low-resolution images covering large areas.
Good for monitoring weather.
Image format: 512 x 512 pixels.
Primary lens diameter: 30mm.
Purpose: The Cadillac of imaging cameras, the WFHRPC is designed to
provide extremely high-quality images from flyby where there is not enough
time to get many single images. Includes the color filters, and also some
advanced radiation shielding and error-correction. Expensive and heavy.
Image format: 1024 x 1024 pixels.
Primary lens diameter: 50-150mm (adjustable with stop).
Detailed description: Optical imaging is performed by two families of detectors: vidicons and the newer charge coupled devices (CCDs). Although the detector technology differs, in each case an image is focused by a telescope onto the detector, where it is converted to digital data. Color imaging requires three exposures of the same target, through three different color filters selected from a filter wheel. Ground processing combines data from the three black and white images, reconstructing the original color by utilizing the three values for each picture element (pixel). A vidicon is a vacuum tube resembling a small CRT. An electron beam is swept across a phosphor coating on the glass where the image is focused, and its electrical potential varies slightly in proportion to the levels of light it encounters. This varying potential becomes the basis of the video signal produced. Viking, Voyager, and many earlier spacecraft used vidicon-based imaging systems. A CCD is typically a large-scale integrated circuit which has a two-dimensional array of hundreds of thousands of charge-isolated wells, each representing a pixel. Light falling on a well is absorbed by a photoconductive substrate, such as silicon, and releases a quantity of electrons proportional to the intensity of the light. The CCD detects and stores an accumulated electrical charge representing the light level on each well. These charges are subsequently read out for conversion to digital data. CCDs are much more sensitive to light of a wider spectrum than vidicon tubes, they are less massive, they require less energy, and they interface more easily with digital circuitry. Galileo's Solid State Imaging instrument (SSI) contains a CCD with an 800 x 800 pixel array. The cameras on the Mars Observer spacecraft were unique in that they employed a single-dimensional CCD array. The orbital motion of the vehicle over the surface of Mars supplied the second dimension required for image formation.
Purpose: Allows images to be taken in different wave bands, to form color images, and very low-resolution "spectra". Necessary with the imagers to produce color images. May also include special narrow-band filters for line emission particlular to the target, or polarizing filters to study the texture of rock, etc.
Detailed description: A set of wide or narrow band filters designed to cover near-UV to near-IR wavelengths. The are mounted on a rotatable filter wheel to allow them to be brought in front of the CCD chip. It is also possible to use narrow-band filters tuned to specific spectral lines to make an image in that line (eg. H Alpha). Note that the filters use the imager's DPU, so do not require an extra processor.
Careful analyses of images taken through polarizing filters allow inferences about the composition and mechanical structure of the objects reflecting the light, such as various chemicals and aerosols in atmospheres, ring arcs, and satellite surfaces reflect light with differing polarizations. The molecules of crystals of most materials are optically asymmetrical; that is, they have no plane or center of symmetry. Asymmetrical materials have the power to rotate the plane of polarization of plane-polarized light. Note that the polarizing filters use the imager's DPU, so do not require an extra processor.
Purpose: Measures light intensity at one point at a time. Intensity of light tells composition of object at that point.
Detailed description: Spectral photometers are optical instruments that measure the intensity of light from a source. They may be directed at targets such as planets or their satellites to quantify the intensity of the light they reflect, thus measuring the object's reflectivity or albedo. Also, photometers can observe a star while a planet's rings or atmosphere intervene during occultation, thus yielding data on the density and structure of the rings or atmosphere.
Purpose: Irradiate a sample of rock (must be in contact) and analyze induced radiation using X-Rays. Designed for use on a microrover. Tells what minerals make up the object.
Detailed description: Based on the successful APXS on the Mars Pathfinder Mission and carried by its rover "Sojourner".
This elemental composition instrument consists of alpha particle sources and detectors for back-scattered alpha particles, protons and X-Rays. The APX Spectrometer will determine elemental chemistry of surface materials for most major elements except hydrogen. The analytical process is based on three interactions of alpha particles with matter: elastic scattering of alpha particles by nuclei, alpha-proton nuclear reactions with certain light elements, and excitation of the atomic structure of atoms by alpha particles, leading to the emission of characteristic X-Rays. The approach used is to expose material to a radioactive source that produces alpha particles with a known energy, and to acquire energy spectra of the alpha particles, protons and X-Rays returned from the sample. Such an instrument can identify and determine the amounts of most chemical elements.
The basis of the alpha mode of the instrument is the dependence of the energy spectrum of alpha particles scattered from a surface on the composition of the surface material. The method has the best resolving power for the lighter elements.
Purpose: Takes picture of height, width, and color. Better version of photometer. Views ultraviolet, visible, and/or infrared light (from heat). Tells what minerals make up the object.
Purpose: Like imaging spectrograph, but views X-ray radiation. Gives what elements compose the object instead of minerals. Good for analyzing auroral zones as well as rocky bodies without atmospheres.
Purpose: Like X-ray spectrograph but identifies different elements. It identifies more radioactive elements. Mostly useful for studying small rocky bodies without significant atmospheres, as gamma-rays are blocked by air.
Detailed description: Spectrometers are optical instruments which split the light received from objects into their component wavelengths by means of a diffraction grating. (A good example of a diffraction grating is the common compact disc which stores music or data in microscopic tracks. Observing a bright light shining on its surface demonstrates the effect which diffraction gratings produce, separating light into its wavelength, or color, components.) They then measure the amplitudes of the individual wavelengths. This data can be used to infer the composition and other properties of materials that emitted the light or which absorbed specific wavelengths of the light as it passed through the materials. This is useful in analyzing planetary atmospheres. Spectrometers carried on spacecraft are typically sensitive in the infrared and ultraviolet wavelengths. The near-infrared mapping spectrometer (NIMS) on Galileo maps the thermal, compositional, and structural nature of its targets using a two-dimensional array of pixels.
Sometimes various optical functions are combined into a single instrument, such as photometry and polarimetry combined into a photopolarimeter, or spectroscopy and radiometry combined into a radiometer-spectrometer instrument.
Optical instrument are sometimes installed on an articulated, powered appendage to the spacecraft bus called a scan platform, which points in commanded directions, allowing optical observations to be taken independently of the spacecraft's attitude. For our missions, this is assumed to be included in the cost.
Purpose: Gives a not-so-great image and distance to object when camera won't work due to clouds or haze.
Detailed description: Some solar system objects that are candidates for radar imaging are covered by clouds or haze, making optical imaging difficult or impossible. These atmospheres are transparent to radio frequency waves, and can be imaged using Synthetic Aperture Radar (SAR) instruments, which provide their own penetrating illumination with radio waves. SAR synthesizes the angular resolving power of an antenna many times the size of the antenna aperture actually used. A SAR illuminates its target to the side of its direction of movement, and travels a distance in orbit while the reflected, phase shift-coded pulses are returning and being collected. This provides the basis for synthesizing an antenna (aperture) on the order of kilometers in size, using extensive computer processing. For a SAR system to develop the resolution equivalent to optical images, the spacecraft's position and velocity must be known with great precision, and its attitude must be controlled tightly. This levies demands on the spacecraft's AACS and requires spacecraft navigation data to be frequently updated. SAR images are constructed of a matrix where lines of constant distance or range intersect with lines of constant Doppler shift. Magellan's radar instrument alternated its active operations as a SAR imaging system and radar altimeter, with a passive microwave radiometer mode several times per second in orbit at Venus.
Purpose: Gives very accurate distance to the object. Used to get topography if keep a constant orbit. Also used for navigation near a planet or satellite. Needs clear line-of-sight to solid surface to work.
Purpose: Older, less accurate version of laser rangefinder. However, it is able to work through cloud cover, unlike a laser.
Detailed description: Radar pulses may be directed straight down to a planet's surface, the nadir, from a spacecraft in orbit, to measure variations in the height of terrain being overflown. The coded, pulsed signals are timed from the instant they leave the instrument until they are reflected back, and the distance is obtained by dividing by the speed of light. Terrain height is then judged based upon knowledge of the orbital position of the spacecraft. The Pioneer 12 spacecraft and the Magellan spacecraft used radar altimeters at Venus. Laser light may also be used in the same manner for altimetry. Laser altimeters generally have a smaller footprint, and thus higher spatial resolution, than radar altimeters. They require less power. The Mars Global Surveyor spacecraft carries a laser altimeter which used a small cassegrain telescope.
Essential components to power and control the instruments.
The spacecraft operation is controlled by on-board expert systems. However, the scientific instruments need their own computers to direct data acquisition and storage.
Purpose: The Data Processing Units on the spacecraft hold the data that will be collected from the instruments and hold the software that runs the spacecraft. You will need one DPU for every three science instruments.
Detailed description: A microcomputer with a fast CPU, memory, and some optical data storage. Contains radiation shielding to survive space environments.
Spacecraft and Vehicular systems need power! You had better supply it. Note that rovers need their own power, as do probes and landers (though they may use rover power when onboard). The orbiter or flyby craft can use the drop-craft power when it is carried, but then will be unpowerd after drop, unless its own power is supplied separately.
Purpose: Collect sunlight and distribute to power spacecraft systems.
Detailed description: Panels made of photoelectric materials are deployed on extendable arms from spacecraft to intercept sunlight and convert to electrical energy. You should calculate the area needed to power the spacecraft at the relevant distance from the star. Note that there will be a lapse in power when the spacecraft is shadowed by a planet. Can be combined with rechargeable versions of ion batteries (at normal battery cost) to use excess power over that needed for systems to charge batteries for dark use. There is also a not insignificant risk that panel deployment may fully or partially fail.
Purpose: Small photo-electric cells to run lander or rover systems.
Detailed description: Smaller and lighter versions of the solar panels, designed for use on soft landers or rovers. Note that without batteries, craft will be unpowered when shadowed or at night. Can be combined with rechargeable versions of ion batteries (at normal battery cost) to use excess power over that needed for systems to charge batteries for dark use. Not space hardened and unuseable on orbiters, flybys, or drop probes (atmosphere or hard impact). Be sure to calculate the area needed the stellar flux at the planet. These cells use expensive materials for durability, lightness, and efficiency (to give effective areas of cm^2) and thus are expensive - best used on planets with high solar flux. Of course, planets with thick atmospheres will obscure sun and solar cells will be useless!
Purpose: Stores power to run spacecraft, probe, lander or rover systems.
Detailed description: Small, inexpensive, and light batteries with reasonably long lifetimes suitable for running spacecraft science systems for a limited duration. Uses metal ion technology for longevity and storage efficiency. Each large cell supplies 10kW hours of power - that is, it can supply 10000 W for 1 hour, or 1W for 10000 hours, or any combination of power*time that equals 10000. Small cells can provide 1kW hour. Note that you can power an orbiter/lander combination with a single battery, but that the orbiter will lose power when the lander is dropped to the planet (assuming the battery is on the lander!) so any orbital experiments will have to be completed before deployment of the lander!
Purpose: Uses nuclear decay heat to generate power.
Detailed description: A long-lived radioactive isotope contained in a shielded canister generates heat which is then used to generate power. The most robust power generation method, with nearly indefinite lifetime (several half-lives of the isotope > 100 yrs), no dependence on solar output or shadowing, and large power generation rate. However, nuclear generators are heavy and expensive!
Communications to Earth (for data delivery) and between flyby and probe, or orbit and lander and rover are assumed to be included in the respective platforms and vehilces. If it is desired to communicate between different concurrent missions, then that capability can also be build into the normal on-board systems at no extra cost. Note that as with normal orbit-to-ground communications, craft will be out of touch when the orbiter is not above horizon (even with VLF).
To give an idea of what sorts of systems might be used, two example technologies are given below. Note that for the purposes of this mission, you need not specify these.
Purpose: Provide high-powered communication between spacecraft and/or vehicles using low-frequency radio waves. On planets with ionospheres, can be used to bounce around curve of horizon, but can be impaired by solar activity.
Purpose: Provide low-powered communication between spacecraft and/or vehicles using high-frequency radio waves. Uses line-of-sight, so will have to be relayed by overhead orbiter between distant vehicles, and will be out of touch when orbiter not above horizon. Relatively insenstive to solar activity. Light and low-power for vehicular use.
Detailed description: Both UHF and VLF transceivers are radio devices for communication. Powers listed in table are peak values when transmitting, and do not operate continuously. Therefore it is necessary only to be able to provide this power instantaneously. The VLF version has the advantage that it can "bounce" off the ionosphere (if the planet has one) to communicate over the horizon, but can be susceptible to solar interference.
Purpose: Protect the spacecraft from intense radiation found in radiation belts or stellar flares.
Purpose: Protect the spacecraft from small dust or meteoric particles.
Purpose: Reinforced superstructure to protect instruments in high pressure environments. Can withstand up to 100 bars.
Detailed description: There are some awfully harsh environments out there. Radiation belts, planetary rings, stellar flares, cometary dust tails, and plasma tubes can be a hazard to the spacecraft systems. Normal spacecraft hulls will crumple under high pressure. Shielding of various sorts may be in order if you plan to encounter these things, or you run the risk of systems failure. Of course, if you run into an asteroid, or even a small meteor, or dive into the Sun, no amount of shielding will help. Most missions can probably do without these, as the normal spacecraft hulls will suffice. These are heavy, so include these if you have extra weight allowance to spare.
These are the probes, landers, and rovers that allow the exporation of the atmosphere and surface of a planet. Communications between components is assumed to be included in package.
Purpose: A heavily pressure and heat sheilded capsule designed to be dropped into a thick atmosphere. Has a parachute or ballon to slow descent (if desired). Radios back telemetry to the orbiter or flyby spacecraft.
Detailed description: Similar to the Galileo probe dropped into Jupiter, or some of the Soviet Venera probes dropped into the Venusian atmosphere, the descent probe can radio back information on the atmospheric structure and composition, given the correct suite of instruments. The probe uses a parachute or in some cases a balloon to slow its descent. With a balloon, it can be made to float at a pre-determined pressure level, though there is a substantial risk of failure, and subsequent dropping of the probe. A parachute version will slowly descend until it hits the surface or is crushed by pressure. In either case, it is destroyed. Will require power source (battery) on board to provide power to run systems once separated from flyby or orbiter.
Purpose: Radios back telemetry to the orbiter or flyby spacecraft before impacting the surface of a planet.
Detailed description: Some of the early Soviet lunar missions used impact probes to crash into the lunar surface. Information obtained during the fast descent can be collected, as well as measurements of the impact zone assuming a soil penetrator was carried. Best used on planets with no or thin atmospheres, otherwise it is likely to burn up on entry. Will require power source (battery) on board to provide power to run systems once separated from flyby or orbiter.
Purpose: Deliver an instrument package and/or surface vehicle safely to the surface of a planet. Must use orbiter - cannot be deployed by flyby.
Detailed description: Uses a parachute and descent rocket system to slow descent to an acceptable speed. The Viking landers that explored Mars, and the lunar Surveyor missions, are examples of soft landers. This is the only way to get detailed information on surface conditions, especially on soil composition and possible microbiotic life. Also necessary to deliver a micro-rover to the surface. Best used on planets with no or moderate atmospheres, and stable surfaces (don't land on a lava flow!). Of course, will not work on planets without a solid surface such as gas giants! If it is desired to land on a greenhouse planet such as Venus, the lander must include pressure shielding, or it will fail very soon after landing. Even with such shielding, it is likely to not last very long under high temperature and pressure conditions. A standard lander can stand up to about 30 bars for extended periods, and 50 bars for several hours. Will require power source (battery or solar cell) on board to provide power to run systems once separated from orbiter.
Purpose: Explore the surface of a planet, carrying a small instrument suite over reasonabe terrain. Requires soft lander to deliver to surface.
Detailed description: Scaled-down versions of the Apollo lunar rovers, and automated, the micro-rover can navigate over smooth or moderate (lunar or Martian) terrains. Similar to the Mars Pathfinder vehicle. Difficult terrains can slow or halt movement. Unable to work on unstable or molten surfaces. Beware of high winds! Will require power source (battery or solar cell) on board to provide power to run propulsion mechanism.
Instrumentation adapted from the NEAR project, and the NASA Missions page.
Mission Homepage ---
smyers@nrao.edu Steven T. Myers