Friday, December 11, 2009

New Mars Sample Return Mission - Part Two

This entry continues Bruce Moomaw's description of the new plans for a Mars Sample Return.  The first part can be found here.

Background: At the last meeting of the Mars panel of the Decadal Survey, a detailed plan for conducting a Mars sample return.  The slides have not been posted, but Bruce Moomaw acquired a copy and wrote the entry below.  If you are interested you can watch the presentation, although video and audio drops out fairly frequently and at some key points.  Go to and fast forward through the first three presentations (although the third is an excellent rational for doing a sample return).

The second theme that turns up in Fuk Li's recent presentation to the Mars panel of the Solar System Decadal Survey project regarding the design of a Mars sample return (MSR) mission is how much preliminary research has already been done on the possible design for it -- and the extent to which these efforts have already led to preliminary strawman designs for its components.  As Dr. Li says, some desirable technologies -- working rovers, the MSL's "Skycrane" landing system, aerobraking into a low circular Mars orbit -- have already been developed, and that  while "we do have remaining technical challenges, I believe we have identified them and that we have defined technology plans" to deal with them.  A few examples:

(1)  Li regards development of the Mars Ascent Vehicle as the single most difficult remaining task associated with the MSR mission: "We have not built and flown this rocket", and his chart rated its technical development difficulty as "high".   However, repeated studies since 2001-02 have already done a surprising amount of preliminary work on its design; three industry studies converged on a strawman design for it which was approved as feasible by JPL's "Team X" group and the Marshall Space Flight Center, and this has been confirmed by other studies since.  Li still stated that its final development will likely take another seven or so years: three years to recheck various possible alternative designs (some perhaps using liquid rather than solid fuel) before settling conclusively on a final one, and four years to actually develop the chosen system and flight-test it in Earth's upper atmosphere.

The strawman concept is a slim two-stage rocket, weighing about 300 kg (including a 40% margin), and standing about 2.5 meters high, with its two stages using already long-developed STAR solid motors and liquid-fueled attitude thrusters.  During its stay on the Martian surface it would be encased in a slim heated "igloo" to protect its propellant from the effects of Mars' cold.  It would lie on its side, allowing the mechanical arm on the Lander to remove the cylindrical sample container from the returning sample "Fetch Rover" and load it into the spherical Orbiting Sample Canister located on the MAV's top; and then it would be elevated into a vertical position to take off out of the opened top of the igloo.

(2)  The second-most difficult remaining technical challenge for the Mars sample return mission is the development of its anti-contamination systems, to avoid both "forward contamination" of Mars (especially the sampled material) by Earth contaminants on the landed vehicles, and "back contamination" of Earth by Martian material that is on the surface of the sample containers or has been released from a ruptured container.  Li's chart rated the likely technical difficulty of both phases as being in the "medium" range.  He stated that forward contamination will be avoided not by the difficult technique of sterilizing each entire landed vehicle, but by the technique used on the Phoenix Mars lander: sterilizing all the components on the MAX-C sample collecting rover, the Fetch Rover, and the sample-return Lander that are likely to come into contact with the sampled materials, sealing them after "clean assembly" inside "biobarriers" that will be removed after landing, and using less rigorous clean-assembly techniques to minimize the number of microbes or organic contaminants on the rest of the landed spacecraft.

Unfortunately, Li was vague on the likely techniques that would be used to minimize the risk of back-contamination of Earth by Martian material.  He did note that precautions against this will likely be built into both the sample-return Lander and Orbiter, and that the sample container removed from the Fetch Rover will be implanted in the Orbiting Sample Canister using a "double-seal" technique.

(3)  According to Li, a surprising amount of promising work has already been done on the seemingly difficult task of having the sample-return Orbiter locate and rendezvous with the tiny Orbiting Sample Canister that will be launched back into orbit around Mars from the planet's surface by the Mars Ascent Vehicle, and capture the Canister so that it can be loaded into the heat-shielded Earth Entry Vehicle capsule carried on the Orbiter.  The current plan is, in fact, to use cameras on the Orbiter to locate the Canister at a distance of up to 10,000 km away -- with the first-stage development of such a camera already carried on the Mars Reconnaissance Orbiter -- although the Canister will carry a simple radio beacon as a backup for long-range tracking.  After carrying out an automated rendezvous, the Orbiter will "dock" with the round Canister by scooping it up in a conical retrieval basket and funnelling it into the EEV capsule.  Li says that many of the systems and computer algorithms needed to carry out such a complex operation have already been tested to a considerable degree in Earth orbit by the DARPA military research agency's "Orbital Express" mission that carried out repeated automated rendezvous and docking between two unmanned Earth satellites in 2007.  In a chart of current estimates of the difficulties likely to be encountered in developing various technologies for the sample-return mission, unmanned rendezvous and retrieval was ranked in the "low to medium" level.

(4)  There is great confidence in the existing design of the Earth Entry Capsule, which underwent drop tests as far back as 2001.  It would not use a parachute, but would instead nestle the OS canister inside a thick layer of crushable material that would protect it against the full-speed crash of the EEV onto Earth's surface -- a design that both saves weight and actually improves protection from any rupture of the sample container by avoiding any risk of parachute failure.

(5)  The Returned Sample Handling Facility that would store the samples for protection and study -- as well as appraising them for possible hazards prior to releasing them to outside facilities for further study -- has already undergone competitive engineering studies by three different firms in 2003.  It would operate at a "Biosafety Level" of BSL-4, like some existing facilities, and apparently there are no great difficulties likely in designing of building it -- although the sooner the process is begun the better.

(6)  A few other notes:

            (A)  All three of the spacecraft involved in the current design of the sample-return mission -- the MAX-C rover, the Orbiter and the Sample-Return Lander -- would be launched on Atlas V 551 boosters.  (An error in my previous report: the SR Lander, under the current design, would be launched in 2024 -- only two years after the Orbiter -- rather than in 2026.  In any case, the MAX-C rover would almost certainly be dead by the time the Fetch Rover shows up, which will not stop the latter from retrieving its container of cached samples.)

            (B)  The MAX-C rover, the Fetch Rover and the Lander platform would all be powered by solar arrays, unlike the Mars Science Laboratory.

            (C)  The plan is to improve the computer algorithms for driving the MAX-C and Fetch Rovers beyond those on the Mars Science Laboratory, allowing them to drive a minimum of 200 meters per day instead of just 65 meters minimum.  This would be done by allowing the rovers to process their images for navigation purposes while they were actually moving, rather than forcing them to stop at intervals for such processing.

            (D)  Four studies conducted this year by different industrial groups instill confidence that a reliable way can be found for the MAX-C rover to extract rock cores and cache them in its sample container.  The tentative plan is for it to collect 30 10-gram rock cores, probably from three to five overall locations during its drive.

Finally, there is the burning question of the cost of this mission.  Dr. Li reported the results of three recent mission cost estimates, all of them in 2015 dollars.  Two were provided by JPL's Team X group and the the independent Aerospace Corporation, both of which tried to estimate costs down to about 100 million dollars.  The third estimate came from studies by analogy of the different main components of this mission with earlier spacecraft, such as MRO and MSL (although all the cost estimates made an attempt to incorporate the unhappy recent experiences with serious cost overruns on the MSL).  As one might expect, this third estimate was a lot rougher, calibrated only down to about a half-billion dollars. 

Team X and the Aerospace Corp. both estimated the likely cost of MAX-C at $2.1 billion; the study by analogy pegged it at about $2 billion.

Team X and Aerospace Corp. estimated the orbiter at $1.1 to 1.3 billion; the analogy estimate was about $1.5 billion.

Team X and Aerospace Corp. estimated the sample-return lander at $2.3 to 2.4 billion; the analogy estimate was a good deal higher at $3 billion.

Finally, separate estimates of the cost of the Sample Handling Facility pegged it at about $300 to 500 million.

The sum-total estimates by Team X and Aerospace Corp. estimated the total cost of this mission at $5.9 to $6.2 billion; the rougher (but perhaps more trustworthy) estimate by mission analogy put it a good deal higher at about $7 billion.  Repeats of such a multi-part mission would cost a good deal less, since so much of the first  mission's cost would consist of its initial design and development -- but it's clear that we are talking about the sort of thing that cannot be done more than about once per decade, and which during that decade would be likely to completely consume the costs of the Mars Exploration Program -- something that must be taken into account when deciding whether to go ahead and ask Congress to approve this ambitious mission.

1 comment:

  1. IT WILL NEVER HAPPEN!!!!!!!!!!!!!!!!!!!!!