Rover's Trek Around Red Planet Delayed (NASA - 'Spirit')

IOL ^ | 1-8-2004

[blam]

"Not a creosote bush in sight. Can't have the western desert without those damn things."

I've read that a cresote bush has been determined to be the oldest living thing on earth.

[Professional Engineer]

At least they lander has the ability to lift it back up. I could easily envision the ramp having a single deploy, with no retry capabilty.

[discostu]

I wouldn't be suprised, the damn things are hard to kill, part of why they're everywhere

[lepton]

I don't get this. If something is blocking it now, it'll still be there 3 days from now.

They aren't just waiting for the air-bags to go away. They are waiting for the power, and communications availability to roll the airbags up a bit more. As I recall, the lander and rover take about 10 days to reach a full charge after the exertion of unfurling. That initual event only rolls the airbags partially, as it was hoped that would be sufficient to allow the rover passage. It wasn't, so they'll build up more power so as to wrap the bags a bit tighter.

[theDentist]

Thanks both!

[apillar]

The way that one of the experts explained the problem was that they weren't worried that the rover couldn't drive over the airbag, (the rover can drive over obstruction up to 10 inches high). The were worried that the airbag might snag on the solar panels and damage them or entrap the rover. The chance of this happening is very slim, but they aren't willing to risk it when there are several other options open.

[Paradox]

The chance of this happening is very slim, but they aren't willing to risk it when there are several other options open.

I Was about to write the same thing. I am fairly certain that the rover could drive over it all, no problem, but even if there is a 1% chance of failure, they have to take measures to make sure as possible.

Then again, they could always just have the special effects guys go in and shove the rover a bit :)

[blam]

"The chance of this happening is very slim, but they aren't willing to risk it when there are several other options open."

I agree with the 'go-slow' decision. We've spent $800M and waited 7 months...what's a couple more days to get it right. There's no guarantee that we will be as lucky on the Opportunity landing as this one.

[hattend]

If scientists are unable to clear the path, Spirit can roll down either of two other ramps. Those maneuvers would require the rover to perform a robotic pirouette, however, to ensure it faced the right direction.

Why delay it then? Do the pirouette and get it off the lander. Serves two purposes: Get's the mission underway and it makes sure the rover drive wheels work.

[William Tell]

hattend said: "Why delay it then? Do the pirouette and get it off the lander. Serves two purposes: Get's the mission underway and it makes sure the rover drive wheels work."

Others have pointed out issues regarding recharging the power system as a reason to delay.

Generally, there will be reason to delay whenever there is more than one option for proceeding.

Both the idea of rolling down the ramp with airbags possibly obstructing and the idea of a "robotic pirouette" have risks associated with them.

For example, although the rover is able to perform a pirouette, the perfection of the maneuver depends upon each wheel performing properly. If one of the wheels drags when it is supposed to roll, then the maneuver that is intended to keep the center of the rover stationary would instead cause the rover to move unexpectedly in some unpredictable direction an unpredictable amount.

This unpredictable motion might be of little concern when the rover is out in an open area and once the problem has been diagnosed, such motions can be predicted and taken into account.

However, prior to such diagnosis, this unpredictable motion might cause the rover to tumble off its platform and it might land nearby in a position which could render it immobile.

These hypothetical risks have to be weighed against the risks associated with possibly becoming entangled in a non-retracted airbag.

If there is a zero-risk option aimed at further retracting the airbags, then neither of the risks associated with non-optimal movement of the rover needs to be faced.

Weighing these various risks and deciding which might be the proper one to face is a job for the ground crew and it takes time to analize such scenarios. With the success of the whole mission hanging in the balance, there is little reason to hurry.