Would Phoenix be able to blip its rockets to move around a bit?, ...and not just pulling itself along with the arm... Options

[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.

[djellison]

5 seconds post landing, the pressurizing helium gas of the prop system is vented, so it's a no from the start. If you look at the realtime EDL movie at the Phoenix website, this is shown.

Doug

[ToSeek]

One of the Surveyors (unmanned lunar landers) did a "hop" using its rocket engines. I think that's the only time such a maneuver has been planned or attempted.

[ElkGroveDan]

There was some talk of doing this with NEAR after its touchdown on Eros, but nothing came of it.

[kwan3217]

As noted before, once the helium vents, Phoenix is where it will be when the next expedition will find it. Besides the helium, once the panels are deployed (one-way) the balance is thrown off.

But, does it make any sense to have a capability like this? I can see some lander landing, then using its cameras to see a spot 20m away where there is ice on the surface or a tree growing, then hopping over there. Phoenix is predicted to only use 40-45kg of the 67kg of propellant loaded. It should be possible to fly 20m or so with the fuel left. Once it's on the ground, if it were to fly again its landing ellipse would be meters or centimeters across instead of kilometers.

And why is the helium vented so soon after landing? It must be really high priority to be that early.

[djellison]

And why is the helium vented so soon after landing? It must be really high priority to be that early.

It makes sense, I guess, to get rid of any pressure as soon as possible, so that fuel line heaters etc can be turned off and not bothered with again. While the system is still pressurized, you can't let the fuel freeze, which it would do quite quickly, I would have thought, with -60degC outside or whatever it will be. Just guessing, but that's my take.

I would rate the chance of seing a tree growing as somewhat slim (particularly given that such a thing would be easily visible from HiRISE)

The point with Phoenix is that you really don't need mobility. The science is right under your feet wherever you end up. If you need mobility - rockets are a dangerous, heavy complex and unpredictable means of doing it. For missions that need mobility ( MER, MSL ) then they've got it.

Doug

[dmuller]

... so that fuel line heaters etc can be turned off ...

My guess too is that the electric power budget overrides the slim possibilities of having the chance of a hop that saves the mission. Phoenix will be landing just before night fall, and they even switch off the lander radio one minute after touchdown, arguably to save energy until the solar panels are deployed and the sun rises again. And heating up the fuel at a later stage may just consume too much energy

[tasp]

Perhaps future landers might have a more volatile fuel (under Mars conditions) and that could be bled off instead, and saving the helium for blasting the dust off the solar panels every year or two.

[nprev]

I dunno, man. Correct me anyone if I'm wrong here, but the helium is a pre-load to provide sufficient pressure to assure delivery of the hydrazine to the thrusters (where regulators/restrictors/whatever step it down to the correct throughput). This is a pretty mechanically complex and obviously mission-critical system.

I can't see anybody signing off on additional plumbing & complexity to reutilize the helium after landing; too many scary potential failure modes. Blowing N2H4 all over the panels during flight accidentally is one off the top of my head...ugly enough, but worst case is a dead-open leak that either bleeds out all the fuel or reduces the tank pressure below levels needed for safe landing...splat.

Any sort of solar-array cleaning system has to be independent.

[Guest_Oersted_*]

The point with Phoenix is that you really don't need mobility. The science is right under your feet wherever you end up. If you need mobility - rockets are a dangerous, heavy complex and unpredictable means of doing it. For missions that need mobility ( MER, MSL ) then they've got it.

Doug

I think that is just plain wrong, the argument about not needing mobility. We can be in the very fortunate situation that everything is right where we want it, but it also might possibly not be the case.

The rovers have shown us that mobility is the only way to go. Those little wheels have enhanced the science return immeasurably. Even Phoenix would be able to to do ten times more science with just limited mobility. It is a left-over from another, more limited, era of space exploration.

[pioneer]

Phoenix will be landing just before night fall, and they even switch off the lander radio one minute after touchdown, arguably to save energy until the solar panels are deployed and the sun rises again.

Doesn't Phoenix land at the time of year when the sun is up nearly the entire Martian day?

[djellison]

. Even Phoenix would be able to to do ten times more science with just limited mobility.

Really? With only 90 sols, 8 TEGA ovens and 4 MECA suites? At a site where all the obital data says the science we are after is essentially homgenous across the ellipse. Ten times more science? Please do explain how, exactly.

I would argue the EXACT opposite of what you say. There would be ZERO scientific benefit for Phoenix to be mobile. Would a rover in the polar plains be interesting and exciting? Yes. For most science investigations on Mars is mobility a benefit? Yes, clearly, MERA and MERB have shown this to be the case. Would a rover offer benefits for the science that Phoenix is attempting? No. Phoenix has a full schedule to conduct as thorough a characterization as it can manage within the time of it's expected life span. Phoenix is niche, it's arguably one of the few scientific missions to Mars that doesn't need mobility ( a second being the long overdue net-lander type mission).

But to claim that Phoenix would be able to do 'ten times more science with just limited mobility' is wrong - very very very wrong.

Doug

[djellison]

Doesn't Phoenix land at the time of year when the sun is up nearly the entire Martian day?

At the time of landing, it will be up all day. I guess human nature just means we call 5, 6, 7pm 'evening' even though, when it's still daylight at midnight, it isn't.

[pioneer]

I think that is just plain wrong, the argument about not needing mobility. We can be in the very fortunate situation that everything is right where we want it, but it also might possibly not be the case.

The rovers have shown us that mobility is the only way to go. Those little wheels have enhanced the science return immeasurably. Even Phoenix would be able to to do ten times more science with just limited mobility. It is a left-over from another, more limited, era of space exploration.

I thought at one point the mission did have a rover, called Murie Currie, like MPF when it was originally scheduled to launch in 2001 but was removed to due the budget.

The point of this mission is not to see pretty scenery but to examine the soil and search for water. Although having mobility would make the mission more exciting to the public, the landing area will be flat and homogeneous for as far as any mobile robot could travel. You would essentially be seeing more of the same everyday.

[Alex Chapman]

I think that is just plain wrong, the argument about not needing mobility. We can be in the very fortunate situation that everything is right where we want it, but it also might possibly not be the case.

The rovers have shown us that mobility is the only way to go. Those little wheels have enhanced the science return immeasurably. Even Phoenix would be able to to do ten times more science with just limited mobility. It is a left-over from another, more limited, era of space exploration.

You really can’t underestimate the ‘vertical mobility’ that Phoenix has. Most of the scientific discoveries made by the MERs have been due to looking under the dust covered surface of Mars. Opportunity’s evidence for a past damp Mars is through rock stratigraphy exposed by craters and Spirit has used the meagre trenching ability of its wheels to expose sulphates.

Phoenix is the first lander that will be able to see virgin material that has not been directly exposed to the Martian atmosphere. It’s going to be able to dig down to up to 0.5m! If Opportunity had been able to do that and look at samples as it dug down it would have made most if not all of its discoveries without the need to drive.