Deep Space 2 Options

[The Messenger]

What do you suppose is the likelihood of the opposite scenario? Instead of going crunch against a surface that was too hard, could the DS2s have been buried in a Martian snow drift? Would that have degraded the radio signals enough to make them undetectable?

Interesting thought. Studies indicate most of the Martian snow is "hard pack":

http://www.space.com/scienceastronomy/sola...w_011206-1.html


I don't know how 'hard' CO2 will pack in a low pressure environment: My personal experience suggests 'not very'. Based upon Opportunity's trouble with Martian sand, I don't think getting buried in a sand dune can be ruled out, either.

As Bruce said, there are many possibilities. Meanwhile, I get to identify threads of commonality.

[Guest_BruceMoomaw_*]

Actually, it was overboard of me to bring up "Hoaglandites" -- but, really, there is no doubt whatsoever as to the strength of gravity in the outer Solar System, and there hasn't been for centuries. (That's how they found Neptune, remember?) Doubting that there is comes perilously close to Hoaglandism.

[djellison]

And anyway - the phrase is Hoaglanderati



Doug

[edstrick]

The Messenger:
"Interesting thought. Studies indicate most of the Martian snow is "hard pack":
I don't know how 'hard' CO2 will pack in a low pressure environment: My personal experience suggests 'not very'. Based upon Opportunity's trouble with Martian sand, I don't think getting buried in a sand dune can be ruled out, either."

Because the martian atmosphere is mostly CO2, there are a lot of opportunities for vapor-transport in the snowpack and rapid grain growth. There've been studies in the last few years based on Global Surveyor thermal mapping of the polar cap ice including low-emissivity regions I think they've decided are glare-ice. You may get a lot of direct frost formation in the polar night directly into solid ice on the cold surface, radiating into space. Lidar data from the Laser altimiter do show polar night clouds, but they're not a massive constantly snowing CO2 cloud cap.

I'm sure there's been a lot of theoretical and data-analysis work on this the last few years that get absolutely zero press, unlike the "banyan trees" that Hoaxland and their dupes <including poor Arthur C. Clarke> have interpreted from the bizarre images of areas that are losing the winter CO2 cover

[Bob Shaw]

And anyway - the phrase is Hoaglanderati



Doug

Doug:

My classical studies are not what they once were, but might it not properly be Hoaglandii Hoaxerus Maximus?

That is the dwarf variety, though, which favours being planted in a south-facing pit (nothing unseemly, no more than 60 ft deep).

Bob Shaw

[gallen_53]

The DS-2 concept of using a 45 deg. sphere-cone from atmospheric entry to impact was very clever. The 45 deg. sphere-cone with a hemispherical back shell is one of the few shapes that can be statically and dynamically stable all the way from orbit to impact. For example, the 70 deg. sphere-cone used with Viking, Mars Pathfinder and MER becomes dynamically unstable at around Mach = 1.8. If a parachute is deployed at that Mach number or higher then the 70 deg. design is better than a 45 deg. design because the greater bluntness means less thermal protection mass and the parachute can be deployed at a higher altitude (very important with a Mars lander). My main quarrel with the DS-2 concept was the use of a surface impacter. With a surface impacter, you're always at the mercy of "Murphy's Law", e.g. whacking into a big chunk of basalt. Historically, Mars always punishes the designer if a significant probability for failure is allowed. I like the idea of reusing the basic DS-2 aeroshell but rejecting the surface impacter. Instead I believe an "airbag decellerator" should be used instead. Normally with a Mars lander there is a mortar in the back shell that deploys a parachute. Replace the parachure with a kevlar fabric inflatable sphere. Have a helium bottle in the aeroshell and connect the bottle to the airbag with a braided stainless steel hose. Attach the hose to the airbag with a quick release that detaches when a certain pressure is reached in the airbag. Program the probe to mortar out the airbag at about Mach 3. The airbag would initially be flailing away behind the aeroshell, attached to it by the braided stainless steel hose. The airbag is slowly inflated until reaching its full shape and then detached from the aeroshell. The aeroshell would then proceed to destructive surface impact. Some quick-and-dirty numbers reveal that an airbag without payload would have a terminal velocity on Mars of about 35 MPH. Now suspend a very small payload at the airbag's center with kevlar strings and copper wires (to act as a dipole antenna). I estimate that one could get a 100 gm payload on the surface of Mars this way with the payload remaining within the inflated airbag after surface impact. Can any science be done with this sort of lander? At the very least it could be used for acquiring an atmosphere snapshot, i.e. acquiring a density versus altitude model of the atmosphere for that specific time and location on Mars. The aeroshell could carry an inertial measurement unit that measured the deceleration force. From the deceleration force it is possible to back out the local free stream density. The history of this deceleration force (atmospheric density versus altitude) could be stored in a flash memory that was part of the 100 gm payload within the airbag. After surviving impact, the 100 gm payload could uplink its data to a spacecraft orbiting Mars, e.g. MRO. The 100 gm payload would be simply a battery, a radio transmitter, the flash memory and timer. The payload would only transmit data when the timer indicated that an orbiter was overhead. You might be able to throw in a CCD camera as well for some surface images. I see this basic design as the ultimate low cost Mars lander.

Gary

[Guest_BruceMoomaw_*]

There have indeed been quite a lot of abstracts on the physical consistency and growth patterns of the polar caps -- and, yes, the puzzlingly dark but cold "Cryptic" region of the south polar cap is now thought likely to be solid CO2 ice. The rest of the cap seems looser -- for meteorological reasons that are still unclear -- but it could still be fairly hard, and certainly the permafrost could be.

But keep in mind that back in the 1970s, Sandia Labs -- the main penetrator enginers -- were routinely crashing large penetrators into solid granite in the New Mexico desert with a wide variety of instruments -- including seismometers 100 times more sensitive than the ALSEP ones -- and having them survive just fine. There is no reason to think that the penetrator concept won't work equally well on other planets, provided NASA doesn't stupidly underfund their development and testing. The latter was almost certainly DS-2's Waterloo.

[edstrick]

I never saw a "final investigation report" on the DS2 debacle, but the summary was basically that the probes should never have flown: "Not ready for Prime Time", in effect. Design was deficient, testing was deficient, I don't recall if they thought assembly was deficient.

(nods at Bruce) Yeah.. there was a lot of work on "Terradynamics" for penetrators. starting with vietnam era seismic traffic listening javelins for besides the HoChiMinh trail.

Don't forget Mars 96 carried (I think 2) substantial penetrators, with considerable instrumentation and afterbodies to be left on the surface with antenna and additional instrumentation. Damn shame that mission never launched properly.

[Guest_BruceMoomaw_*]

I HAVE seen the final DS-2 report, and they thought EVERYTHING was deficient -- including a failure to determine whether the assembly was deficient or not by doing the most elementary testing. I'll see if I can hook the report's URL, but I know I have it on my CD-ROMs.

Yes, Mars 96 had two fair-sized penetrators in addition to its two small surface hard-landers. However, it was excruciatingly clear even before the launch (and commented on in many news articles) that the Russians were so short on funds, and had therefore skipped so many tests, that it would have been an absolute miracle if the spacecraft had worked even if it had been successfully launched. So help me God, they were assembling it in rooms lit by GAS LANTERNS.

[gallen_53]

Bruce Moomaw said

But keep in mind that back in the 1970s, Sandia Labs -- the main penetrator enginers -- were routinely crashing large penetrators into solid granite in the New Mexico desert with a wide variety of instruments -- including seismometers 100 times more sensitive than the ALSEP ones -- and having them survive just fine.  There is no reason to think that the penetrator concept won't work equally well on other planets, provided NASA doesn't stupidly underfund their development and testing. 

We have a ballistic range faciity at where I work. The acceleration experienced by a model launched from a light gas gun is comparable to what a surface penetrator might experience whacking through a chunk of granite at supersonic velocity. A few months ago, I went through the process of proposing the incorporation of a Motorolla 68HC11F microcontroller into a ballistic range model. With some rye amusement, I was politely told by our ballistic range expert that my proposal was technically unfeasible. The accelerations in a light gas gun are unbelievable (over 100,000 gravities). Reports that Sandia has pierced granite with surface penetrators carrying electronics should be treated with some skepticism. The accelerations experienced in a military (powder) gun are much less than a light gas gun. The electronics in a military penetrator might be as sophisticated as a microprocessor but are more likely to be some very simple electronic circuit optimized to withstand high accelerations (a warhead fuze). Also, more likely than not, the military penetrator is a meter long sharpened slug of depleted uranium with the electronics package mounted in the rear. The granite penetrating power of a depleted uranium slug compared to a DS/2 science package is an apples-and-oranges comparison. Did JPL ever launch a DS/2 science package into a basalt boulder? What were its survival statistics? If the experiment was never performed then the concept has no credibility.

[Guest_BruceMoomaw_*]

I didn't say it was a DS-2 sized penetrator -- these were big penetrators, 1-2 meters long, with their entire front third or so being sharp-nosed solid steel. The NASA Technical Report on this subject was published all the way back in 1977, and they succesfully tested a wide variety of science instrument types on them. I'll see if I can dig it out.

[Bob Shaw]

I didn't say it was a DS-2 sized penetrator -- these were big penetrators, 1-2 meters long, with their entire front third or so being sharp-nosed solid steel.  The NASA Technical Report on this subject was published all the way back in 1977, and they succesfully tested a wide variety of science instrument types on them.  I'll see if I can dig it out.

Bruce:

The BIS Spaceflight Magazine also carried a couple of articles at about that time - and yes, they were *big*.

Bob Shaw

[The Messenger]

http://www.jpl.nasa.gov/marsreports/mpl_report_1.pdf

The probes were expected to strike the surface with an impact velocity of about 200 meters per second. The aft-body was designed to withstand a peak rigid body shock of about 60,000 g’s; the penetrator, a shock of about 30,000 g’s. The aft-body could operate in temperatures from 0 to –80 degrees C; the penetrator could operate in temperatures as low as –120 degrees C.

...It would be interesting to know what the calculated maximum g force was at 200 m/s, and whether these numbers include engineering margins.


p22

Due to lack of a suitable air gun, a complete system-level impact test of the probe with aeroshell was not conducted. This prevented full characterization of the dynamic interaction between the aeroshell and the probe. The Board believes that there was a risk of structural failure due to the dynamic interaction between the aeroshell and the probe.

It is a shame to invest so much in getting a package to Mars, and not have either enough design testing or in-flight instrumentation to reduce the number of possible failure modes.

[Guest_BruceMoomaw_*]

I see "Messenger" has beaten me to the punch in finding the Polar Lander/DS-2 failure report. (I hereby retract my crack about "Hoaglandites" -- but PLEASE don't question the basic validity of gravitational law in the rest of the Solar System. As Lt. Columbo said about cigars, this is something we DO know about.)

As for the lack of adequate funds for DS-2, this was just another result of the fact that Dan Goldin actually did believe in his squirrelly version of "better, faster, cheaper" -- as opposed to "smaller and more frequent", which is the part of it that actually works.

[Bob Shaw]

I found an interesting image of the two Mars 96 Small Station landers in the .pdf of the NASA 1996 Mars Missions Press Kit. Interestingly, the document mentions that they would use airbag technology (just two big ones) and says (p52) that the same methods were used for the early Soviet Lunar landings in the 1960s! And on p54 there's mention of the twin penetrator probes returning data for a full year after landing...

...these may be just sloppy reporting on the part of NASA, however - unless there were RTGs involved somewhere along the line.

Bob Shaw

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