[X] My Assistant

[Guest_Oersted_*]

OK, premature, premature, but still... After a succesful landing and thouroughly having dug holes and trenches in the original working volume of the arm: how about moving about a tiny bit? - I was wondering if the rocket engines could possibly be used to shift position just a few decimeters at a time. Small blips, which should be so weak that they wouldn´t overturn the lander.

It could also come in handy when the snows come in later in the year and threaten to bury the lander.

A few things would be necessary: no post-landing venting of possible excess fuel (who knows about that?). No permanent disabling of the rockets after EDL. A possibility to stow and unstow the solar panels (ok, that is probably a show-stopper, but just humour me here...). The last would only be an issue if it was thought that small blips of the rockets would raise sufficient dust to degrade the solar panels´efficiency.

Just thinking out of the box here... - And I know it very probably won´t ever happen. But if!

- Well, let us just get this baby down in one piece for now.

[tasp]

Fleshing out my idea a little more:

There apparently is an existing valve that vents the helium, so a piece of pipe on the discharge of that valve leading strategically towards the deployed positions of the panels would not introduce another leak path into the helium plumbing, so there is no impact to the overall reliability re helium pressurization. A failure of that valve post landing leaves us no worse off than we are now.

The existing hydrazine is unsuitable for long term storage onboard due to freezing effects.

However, if a subsequent lander had suitable hypergolic bipropellents (methane, nitrogen tetroxide ??) they could be vented safely though the combustion chamber through the already existing valving, separately, with no impact to the mechanical reliability of the propellent system. There would be a software fault possible that would cause the system to fail, but there are existing similar software failure modes to the existing control system we manage to live with now.

[dvandorn]

Fleshing out my idea a little more:

There apparently is an existing valve that vents the helium, so a piece of pipe on the discharge of that valve leading strategically towards the deployed positions of the panels would not introduce another leak path into the helium plumbing, so there is no impact to the overall reliability re helium pressurization. A failure of that valve post landing leaves us no worse off than we are now.

The existing hydrazine is unsuitable for long term storage onboard due to freezing effects.

A few thoughts of my own...

First off, after you vent the helium, there is no pressure in the tanks. You'd have to add pumps to pump out anything from the unpressurized tanks, and those tend to be heavy enough to preclude their use. (Hence the use of helium to pressurize the tanks so the fuel delivery systems are pressure-fed and pumpless.)

Second, long-term storage of hypergols on Mars is probably not a great idea due to freezing, but only if you ever plan to use the remaining propellants. Otherwise, if you design your fuel tanks and plumbing properly, you can keep the remaining fuel (frozen or otherwise) in those tanks forever. Hypergols, particularly nitrazine and UDMH (unsymmetrical di-methyl hydrazine) were first developed as rocket fuels in the U.S. so you could maintain fully fueled missiles in their silos for months or even years and have them ready to go at literally a moment's notice. Only in later years were the hypergols traded out for solid fuels in American nuclear missiles.

In fact, there is probably significant hydrazine and nitrazine left in the tanks of the Viking landers to this day. AFAIK, no powered landers (including Surveyors, Lunar Modules, Viking landers, etc.) ever actually vented their propellants after landing. They all vented the pressurizing helium, but never the actual hypergols. (Indeed, if you vented your hypergols and they managed to mingle somewhere below your lander, you're going to get more than a "little hop" out of it...)

-the other Doug