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Mars Pathfinder

  * Originally By: Harald Franzrahe
  * Originally To: Alle
  * Originally Re: Mars Pathfinder Frequently Asked Questions
  * Original Area: NASA News And Press Releases
  * Forwarded by : Blue Wave v2.12
                     Mars Pathfinder Questions and Answers
                           Updated 27 November, 1996
 Some of the more frequently asked questions and their answers have been
 posted here for your convenience, and more will be added as they come in.
          General   Launch &   Entry, Descent     Surface   Sojourner
           Topics    Cruise      and Landing    Operations    Rover
 If you'd like to have a question answered by a member of the Mars Pathfinder
 team, please contact:
                                  David Dubov
                           Mars Pathfinder Webmaster
 and it will be passed along to the appropriate person for an answer. Keep
 'em coming!
                                General Topics
 Why was this mission chosen for the       Could this mission stand alone,
 Discovery Program?                        and how does it complement other
 Describe how Mars Pathfinder is unique,   What is being done to make sure
 and how it follows the "better, faster,   it doesn't go the way of Mars
 cheaper" philosphy.                       Observer?
 What planetary protection measures are
 being used on Mars Pathfinder and Mars
 Global Surveyor?
 Why (in your opinion) was this mission chosen for the Discovery program
 versus other proposed missions?
 Mars Pathfinder and the Near Earth Asteroid Rendezvous (NEAR) mission were
 not chosen by the same process as the later Discovery missions. Pathfinder
 was originally designedto demonstration technology for inexpensive entry and
 landing on Mars, as a precursor to a network of landers called Mars
 Environmental Survey, or MESUR. Because Pathfinder was the first mission it
 fell into what was then considered a "Discovery" mission class - that is it
 had to be done for less than $150M in 1992 dollars. The MESUR Network
 missions were never funded, but Pathfinder is now a technology demonstration
 for landers in the Mars Surveyor program. Later Discovery missions are being
 chosen through Announcements of Opportunity and are being developed by teams
 headed by scientists.
 This mission seems to be part of a series starting with the Mars Global
 Surveyor, but those other missions are not part of the Discovery program.
 Could this mission stand alone if necessary? How does it complement the
 other (US and internationally) planned missions?
 Pathfinder is a "Discovery" mission. The Mars Surveyor Program is separate
 from Discovery and will launch one or two missions to Mars at every
 opportunity (every 26 months). Mars Global Surveyor launches in November
 1996, Mars Surveyor 98 will launch an orbiter and a lander in December 1998
 and January 1999. The 98 Surveyor missions are both using Pathfinder
 components, especially the computer and software. The Mars Surveyor 98
 lander is using much of the entry and descent technology demonstrated by
 Pathfinder, including the aeroshell and the parachute. The science from
 Pathfinder will be completely complementary with the Surveyor Program
 science. In fact, the Mars Surveyor 98 lander is using the same camera and
 weather station technology that Pathfinder is using.
 In addition to the U.S. missions, Russia will launch Mars 96 in November
 1996. It comprises an orbiter, two small landers, and two penetrators. There
 is a U.S. experiment on the landers and the landers and penetrators will
 relay data through the Mars Global Surveyor orbiter. Pathfinder carries
 instruments provided by several different countries. The Mars Surveyor 98
 missions also have international payloads, including Russian contributions
 to the U.S. Infrared Radiometer on the orbiter, and to the lander payload.
 The Japanese will fly an aeronomy orbiter in 1998 to study the upper
 atmosphere of Mars. A U.S. instrument is scheduled to be on board this
 Japanese mission.
 We are currently studying the feasibility of a joint U.S.-Russian mission
 called Mars Together in 2001. One option for this mission is for the U.S. to
 launch an orbiter, and to provide a "carrier" spacecraft to be launched with
 a Russian lander on a Russian launch vehicle. We are also studying a sample
 return mission which could be made affordable by partnering with other
 --Donna Shirley, Mars Exploration Program Manager
 Describe your spacecraft and instruments including what is unique, versus
 ones in the past, that allowed it to be built quickly and cheaply?
 The Mars Pathfinder spacecraft is quite different from other missions built
 at JPL. First of all, as a lander mission, the prime focus is on getting the
 lander/rover instrument package safely to the surface of Mars. This means
 that this spacecraft must be able to electro-mechanically transform itself
 autononmously from a "cruise" configuration much like a Galileo (without the
 cruise science observations of course) into a stable science platform on the
 surface of Mars. All of this must be done on a budget quite small compared
 with previous planetary missions. This adds considerably to the technical
 These challenges were met by first taking maximal advantage of past work: we
 "inherited" hardware from the Cassini mission to Saturn; we utilized designs
 of equipment flown to Mars on the Viking missions of the 70's; and we have
 an improved understanding of the environmental uncertainties from science
 observations obtained over the last 2 decades. Secondly, improvements in
 computer technology have allowed us to model, design and test aspects of our
 system that were impossible 20 years ago. Finally, we have built a small
 "Skunkworks-like" team that has accomplished only that work necessary to do
 the mission, with little red tape nor redundancy in effort.
 What is being done to make sure it doesn't disappear like the Mars Observer?
 No one can build a complex spacecraft that is absolutely guranteed to work.
 Embarking on unique, first-of-a-kind enterprises, by their very nature,
 invoke risk taking. However we can go to great lengths within the limits of
 our budget to minimize technical risk. Much like the design process leading
 to a passenger jet, spacecraft designers must ensure that design margins
 conservatively exceed the uncertainty in the expected environment and that
 the spacecraft is tested to those environments. Much work then must be
 placed in understanding the environment, followed by as much testing as
 money and time will allow. We feel quite certain (and many independent
 reviewers have agreed) that although Mars Pathfinder is about 1/10th total
 mission cost of Mars Observer, that we have struck an appropriate balance
 between cost and risk.
 --Rob Manning, Mars Pathfinder Flight System Chief Engineer
 In what way do planetary protection provisions affect Mars lander missions
 (such as Pathfinder) and Mars orbiter missions (such as Global Surveyor)?
 The major impact of the planetary protection requirements on Pathfinder is
 that we must carefully clean the spacecraft before launch in order to keep
 from contaminating Mars. Although scientists now believe that it would be
 difficult to sustain and cultivate life on Mars, they would prefer that we
 not take any chances. They have developed a system for rating different
 missions by the potential impact that they could have. The most stringent
 missions are those which will be returning samples from Mars or are
 performing life detection experiments there. In both cases, complete
 sterilization is required. In our case (and MGS), we are allocated a
 specific number of biologic spores which are deemed acceptable. We have to
 clean the spacecraft (or perform mission design tricks - I write about
 below) to reduce the number of spores below this level (I am glad to say
 that we are well below the acceptable number). The only parts of the
 spacecraft which we actually need to clean is the part that will come in
 contact with the Martian atmosphere and surface. The other parts (meaning
 the third stage and cruise stage) do not have to be cleaned because they
 will either not hit Mars (we specifically bias the aim point of the Delta
 away from Mars so that upper stage does not hit the planet) or will burn up
 during entry (we had to perform a break-up re-entry analysis of the cruise
 stage to prove this will occur). MGS did not have to do any planetary
 protection related cleaning because they can guarantee that the spacecraft
 will not enter the Martian atmosphere for a long time with high probability.
 --Richard Cook
                         Pre-Launch, Launch and Cruise
 Why does Mars Pathfinder    How many pieces in a   Why does the second stage
 launch at 2:09 am?          fairing?               shut down and then start
                                                    up again later?
 When does it enter Earth's  When is the first      How many miles
 shadow?                     two-way commiuncation? (kilometers) will
                                                    Pathfinder fly to Mars?
 While watching pre-launch
 pictures, technicians
 appear dressed in isolation
 suits. Why?
 Why it is that 2:09 a.m. on 2 December (and earlier times on dates
 thereafter) is the precise time Pathfinder must launch? What is is about the
 Earth's position that makes this important?
 When the spacecraft leaves the Earth to go to Mars, it must be going in a
 particular direction. Since the Earth rotates, the launch site is only lined
 up with this direction twice per day (for an instant in each case). Since
 the two opportunities are about 12 hours apart, the launch vehicle people
 make us choose one or the other. It is okay to launch at a time slightly
 different from the ideal time because the spacecraft can use it's propulsion
 system to correct for the error. The spacecraft has a limited amount of
 fuel, however, so we can't accept a very big error (up to approximately 1
 minute is okay).
 You can see all of Mars Pathfinder's launch opportunities at the Launch
 Windows Page.
 Does the fairing of the Delta II rocket fall away in two pieces or more?
 Very briefly, can you explain why the second stage temporarily shuts down at
 9 minutes 20 seconds after launch and starts up again about an hour later?
 The first burn of the second stage is used to place the spacecraft in a low
 parking orbit around the Earth. It then coasts until it gets to the right
 point in its orbit to do the burn to go to Mars. The second stage then
 ignites again to begin pushing the spacecraft towards Mars. The third stage
 finishes off the job because the second stage fuel tanks are nearly empty.
 What is the exact time after launch that the spacecraft enters Earth's
 It depends on launch date. For December 2, we go into shadow at 3:15 am and
 exit at 3:45 am.
 After emerging from the shadow, the first two-way communication between
 Earth and the spacecraft is from "flight managers at JPL" -- is this
 This is not quite correct. The spacecraft begins transmitting when it
 separates from the third stage (at about 3:25 am). The Deep Space Network
 station in Goldstone, California should detect this signal about five
 minutes later, and we should begin to get engineering data from the
 spacecraft. We don't actually try and send a command to the spacecraft for
 several more hours (about 4-5 hours after launch). All of these operations
 are conducted by engineers at JPL.
 --Richard Cook, Mars Pathfinder Mission Operations Manager
 How many miles (kilometers) will the spacecraft fly to Mars, and how many
 miles (kilometers) will the Earth be from Mars on arrival day (4 July,
 Because the path which the spacecraft takes to get to Mars, essentially
 "catching up" to the planet, it will travel approximately 312 million miles
 (500 million kilometers) in its seven month journey. However, when
 Pathfinder actually arrives at the planet, the Earth and Mars will be
 separated by approximately 120 million miles (200 million kilometers).
 --Dave Spencer, Mars Pathfinder Trajectory and Navigation Team Member
 While watching pre-launch pictures, technicians appear dressed in isolation
 suits. Why?
 Technicians and engineers that work in the vicinity of the lander must wear
 what we call "bunny" suits (it was a joke name originally, but many years
 ago the name caught on). These are clean head-to-toe garments that prevent
 dirt and biological contamination of the lander by the workers.
 At other times when the hydrazine fuel was being loaded into Pathfinder's
 fuel tanks, some workers had to wear "SCAPE" suits. These suits are also
 head-to-toe, but they also provide self-contained breathing equipment which
 is strapped to their backs. In fact they look a lot like space suits.
 Hydrazine, in addition to being highly flammable, is an extremely caustic
 and dangerous liquid. These suits are designed to protect the workers in the
 unlikely event of a hydrazine leak.
 --Rob Manning
                          Entry, Descent and Landing
 How can you use such a What has been done to   What is stopping the lander
 small parachute on     ensure successful       from landing on a large
 Mars?                  operation?              rock?
 What stops the         Why is Pathfinder not   Why does Pathfinder use
 parachute from falling landing near the        petal/airbags vs.
 on the lander?         so-called "face"?       traditional landing gear?
 Why is Pathfinder
 landing at night (Mars
 local time)?
 If the Mars atmosphere is less than 1% than that of Earth, how can a
 parachute of the size you are using be sufficient? It would seem to me that
 you would need a parachute close to 1000' wide to achieve the same effect.
 Would you please explain the dynamics of placing a lander on Mars, and why a
 small parachute would work on Mars as it does on Earth?
 You ask a very insightful question. The bottom line is you're right,
 parachutes this small aren't sufficient on Mars! On Mars Pathfinder, as on
 Viking, we use a "small" 40.5 ft (12.5 m) chute. It was scaled so that, with
 our lighter lander, it does about as much for the our descent speed as does
 Viking's. Our terminal velocity seconds before getting to the ground (where
 the atmosphere is "thickest") is still about 65 m/s (146 mph)!!
 You are correct, it would indeed take a a larger chute to get slower
 "normal" Earth-like terminal velocities. Our chute on Mars is about the
 equivalent of a chute 38 times smaller in area on Earth (6.5 ft across!),
 and this includes the effect of Mars' lower gravity! A chute that could
 lower our lander to the Martian ground at a gentle 10 m/s (22 mph) would
 have to have an area about 42 times larger than our "little" chute (or a
 diameter of 263 ft)! That's 42 times the mass (and volume) of our 10 kg
 chute, or 420 kg, more than the mass of our entire lander! It wouldn't fit!
 We would need to have a "gossamer" (ultra-light weight material) parachute
 and then figure out how to get it open at high speeds!
 This is why we turned to solid rockets to stop our lander just before we hit
 the ground. Viking, too, used liquid rockets to slow the terminal decent.
 Also Pathfinder's airbags protect the lander from the local terrain
 variations (bumps, craters, rocks, hills, etc.) after the rockets do their
 So why do we do we use a chute at all? Well, parachutes might not be all
 that good a laying a lander gently down on the Martian surface, but they do
 a spectacular job of braking something moving very fast. Remember, the drag
 FORCE a chute generates (therefore its deceleration), is proportional to the
 square of the velocity and only linearly proportional to the atmospheric
 density; so even a thin atmosphere and a "small" chute will do much to slow
 our entry vehicle down once the heatshield's aerobraking has been mostly
 This is also true of heatshields, our entry vehicle (like Viking's) enters
 the upper atmosphere at 7 km/s (or more than 15,000 mph!). Most of this is
 reduced by the friction with the heathsield. But even 2 minutes later, our
 vehicle is still screaming in at nearly 400 m/s (900 mph) when the parachute
 opens before slowing down to 65 m/s near the ground. I'd say that reducing
 our velocity by a factor of 6 (a factor of 36 in kinetic energy), isn't all
 that bad for only 10 kg of extra payload mass, wouldn't you?
 So, the short answer is, you're right, parachutes don't work on Mars like
 they do on Earth (neither do airbags, but that is another story), but they
 do a great job when you need to slow down something that is whipping through
 the Martian atmosphere FAST!
 --Rob Manning
 As with other missions, the ability to deploy the panels for solar use, high
 gain communications, or any other use for that matter, has not been as good
 as could be. What has been done in ensuring successful operation now or in
 the future? It seems without them opening up all the way it can cause major
 problems. Like Galileo's high gain antenna and Mars Surveyor's 20 degree
 shortfall in deployment of its solar panels.
 The problems associated with moving parts are difficult ones to solve. Since
 the cost to send one kilogram of material into space is so high, spacecraft
 designers must be very stingy in allocating mass to the engineers who make
 the mechanisms. You might be surprised that the typical spacecraft mechanism
 can be destroyed with your bare hands!
 The other part of this equation is that MOST of the time, mechanisms must
 only need do their jobs under rather benign weightless conditions in space,
 BUT they must also be able to handle the much rougher conditions that
 precede getting there: ground handling and launch. It is these phases of the
 mechanism's life that are the most traumatic. They are the most difficult to
 quantify as well. I don't think the designers of the Galileo high gain
 antenna mechanism would have expected that the antenna would be closed for
 so long before finally opened in flight and that it would have had to
 survive three cross-country road trips in a van! (Both of these events were
 a direct result of the Challenger disaster.)
 There is no magic formula for making mechanisms work in all situations, but
 we have been learning just how subtle these problems can be. The trick is to
 learn from your (and other people's) mistakes. Mars Pathfinder has more than
 its share of moving parts. We knew that going in, so we went out of our way
 to be a bit paranoid about it. We hired the very best spacecraft mechanical
 engineers we could find. Going to Mars made the job a bit more difficult in
 some cases because of our need to have the mechanisms work under very harsh
 environmental conditions (harsher even than in deep space). For example, the
 Rover, the IMP camera and the high gain antenna actuators must all work
 under very cold conditions (as low as -90 deg C). Most lubricants do not
 lubricate at those temperatures. We had to make sure that the actuators were
 either warmed before they were used or had adequate torque margins for the
 motor to overcome the sticky lubricant before it warmed up with use. In some
 cases we "overkilled" the problem (e.g. the lander petal actuators) and
 provided much more torque than we thought we really needed - just in case.
 (I could go on and on.) It is safe to say that the mechanisms on Mars
 Pathfinder were a LOT of work. But we tested and tested them (even beating
 them up!) under many rough conditions until we were finally satisfied that
 they will work fine when we need them to.
 What is stopping the lander from "landing" on a large rock, and making it
 impossible to open up the craft to do its thing on Mars?
 We all wondered about this at the beginning. So we tried it! First of all,
 it turns out that we had a hard time getting the inflated, 17 ft beachball
 of a lander close to a big rock! As long as those airbags stayed inflated,
 it wanted to roll away from anything big and pointy. Secondly, even when we
 did manage to coax it right next to a wicked boulder, the petals opened
 right up even if it meant having the whole lander do a backflip! It took
 some work, but we actually made that happen once in our Mars Yard at JPL and
 without damage! It really helped that the petal actuators (a motor and a
 gear train mounted on each of the three petal hinge lines) had the torque
 margin to actually LIFT the lander off of the ground (they can even
 indefinitely support the lander in a sort of "iron cross" once open). And
 these tests were done under Earth's gravity, which gave the rocks a distinct
 advantage. With many many tests behind us, in not one case would it have got
 What stops the parachute from falling onto the craft and gumming things up
 that way?
 Lots of people asked us that question at the beginning. If you don't give
 this some serious thought, there is a real risk that the lander could get
 covered by the chute (a bit more than embarrassing). Fortunately we designed
 the timing and sizing of the solid rocket firing (remember there are three
 mounted inside the backshell) such that when the lander inside its inflated
 airbags comes to a stop some 12 m above the Martian surface, the software
 activates a cutter that cuts away the bridle thereby freeing the backshell
 from the lander. The rockets, with still a quarter second of impulse left
 over, launch the backshell up and away taking the parachute with it (at an
 angle, tumbling as it goes). Meanwhile the lander and airbag go bouncing
 away in the other direction! (Don't you wish you could be there to watch it
 all happen?). You can click here to see an artist's rendition of this
 --Rob Manning
 To satisfy the curious, Pathfinder should have landed near the so-called
 Face/Pyramid area. Or is that a hoax?
 That there is a rock formation on Mars that looks somewhat like a face is
 certainly true, but it is also true there are many similar naturally
 occuring structures on the Earth, Moon and Mars that resemble faces, animals
 and even man-made designs. The best way to see what large geologic stuctures
 exist on Mars is to use the high resolution cameras on board the
 recently-launched Mars Global Surveyor. Mars Pathfinder can not be
 accurately aimed to any site smaller than a typical US county. We are
 specifically targeting the ancient Ares Vallis outflow channel. Fortunately
 the channel is big so we will not miss it! This site is ideally suited to
 Mars Pathfinder's geologic mission. We believe a huge flood carved that
 channel and deposited a large number and variety of rocks from the highland
 water source into the flood basin where we intend to land. Our miniature
 robotic geologist, the Sojourner Rover, will be able to analyse these
 various rock types and give us an idea of how they were formed and about
 Mars' early history.
 In addition, all of the power for the spacecraft is collected from solar
 panels. In order to get maximum power, one of the landing site requirements
 was to have the sun be high in the sky. This restricted the landing site to
 +/- 20 degrees from the equator of Mars. Cydonia (where the so-called "face"
 is located) is at too high of a latitude for the lander to receive adequate
 --Rob Manning

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