Well, that's a tough question. What will happen, for example if Mars Phoenix fails to touch down successfully? Maybe I look a bit pessimistic, but I like to think in perspective. I think that:

1.If MSL managers give up the skycrane and decide to use Phoenix-like pinpoint landing system, it will effectively move the launch date from 2009 to 2011. Since there's no NASA orbiter planned for launch in 2009, maybe we won't have a new spacecraft then.

2. It will end the scout program or... the next scout mission will be a simple orbiter.

3. There will be several small landers in future, using the good old airbag bouncing method.

The next Mars Scout is going to be an orbtier anyway - two are shortlisted of which one will fly. Future multple airbag landers are, I would think, quite likely, something in the Mars Netlander idea.

The Skycrane manouver ( the hardware is a decent stage...the 'eek' moment is a procedure called skycrane) - is not something they've picked for fun - it's something they've picked because it's the best way they can think of getting the payload onto the ground. If it doesn't work with MSL, I wouldn't be suprised to see them try again with a different vehicle a couple of years later.

Doug

I don't understand - I thought the safest way for a big rover is a pinpoint landing using retro rockets...

MSL is a retrorocket landing.

Doug

Pathfinder and then two MER landings demonstrated that airbag-assisted landings are effective. They are three for three which is a far better success ratio than straight retros. Other methods have certainly worked, but given something as uncertain as putting cargo down softly on Mars, when you have an engineering model that clearly works and has been studied to death, it's reasonable to wonder why the powers that be would want to try something that has not been proven to the same degree.

Of course, because there was no telemetry , we don't really know for sure why MPL failed -- never mind that leg actuator rubbish. The landing system may have been perfectly fine.

With MSL it's weight that seems to put the kybosh on an airbag landing. I think the MSL package is even heavier than the Viking landers. I would have thought the airbag-assist concept would have scaled up somewhat though.

With Phoenix, I think a safer approach would have been to airbag it but the engineering team certainly knows best. Maybe it was not possible at the latitudes contemplated.

If either of these were to fail, it's nice to know there is a reliable fall-back landing method.

If space opens up on the launch manifest, why not MER 2.0? We know they work pretty well and we have plenty of low-latitude landing sites to check out.

On the whole, the Mars program is now mature enough that I doubt another lander failure will set anything back too significantly. MRO has showed us so much fascinating stuff that needs to be explored we should be kept busy for decades as long as the American taxpayer keeps footing the bill. On that note, here's to American taxpayers worldwide!

Well, I know, but I meant the old Viking way. I still don't see how they are going to keep a descent vehicle over the surface for a long time while the rover is being laid. Indeed, Spirit used such a technique during EDL, but for a short time.



Errr... Beagle 2 also used an airbag system ( though the official version suggests a parachute failure rather than an airbag failure ).
The Beagle case... The lack of any retro rockets should mean a bigger chance of failure ... if all other systems work.

I'm almost positive that the reason Phoenix isn't an airbag is because Mars Surveyor 2001 Lander wasn't an airbag lander. You'd have to try and figure out why they didn't take that approach to begin with, but I suspect it's due to the relatively unproven airbag technology (At the time), so...

MSL can't use retrorockets because that would create a bit of a crater where it will land, not to mention ruining it's first area to take samples. At least, that's what I've always understood...

It's really not that hard a problem....take the Viking landing - and simply take the terminal decent speed and change it to zero. We're talking more than 30 years later. Phoenix could, technically, enter a hover a few metres above the surface ( not that there would be any point ). MSL is a big challenge, no doubt, but no more so than the orig. challenge of the Pathfinder landing.

The MER engineers are on record - to do airbags bigger than MER just doesn't add up. The ammount of mass you have to dedicate to the landing system is utterly enormous with airbags. To scale from a 180kg rover to a 700kg rover - the airbags and the structure to encase the lander would be many tonnes. Then - if they work with that much weight, you've got yards and yards of airbag material to try and get over to egress onto the surface. Airbags at that scale just don't make sense - period.

http://www.youtube.com/watch?v=q1UKwFfXmUY

Rob explains it best

Doug

Isn't right that the MPL landing profile was chosen before MPF?

Technically the MPL landing design was chosen in the '60s as it was very similar to VIking - the major changes being a switch to pulse motors instead of throttled ones and direct entry instead of entering from Orbit.

Doug

Hm, that was interesting for me to know

It seems that the simplest EDL design is the design of Mars 3. Direct entry to a ballistic trajectory. We know that's working, too So we have three working technologies - airbags, Mars 3 technology and Viking technology.

Also, from what I've read, the airbag concept just doesn't scale up any further than a MER-sized payload. In fact, they were right on the edge of what an airbag system can do with the MERs.

They (our own Mars Engineer, among others -- hi, Rob!) tested the same airbags as used on MPF with MER masses, and the airbags literally came apart at the seams. Several precious kilos of mass went into beefing up the MER airbags to ensure they would work, and the conclusion of all concerned seems to be that you can't land anything much more massive on Mars than a MER using the airbag system.

-the other Doug

This reminds me of the film The Red Planet. I suppose you know it's scored as one of the worst space movies in badastronomy.com The crew survived an airbag landing

My thought exactly. The software has been refined, there are operators with years of experience, there are plenty of sites, and MRO will be very helpful at site selection and preliminary analysis of the actual landing locations.

Well, the 2001 lander was a modified version of MPL, which wasn't an airbag lander, either. Considering Mars Pathfinder didn't land until 1997, one can see why they didn't build on its technique before they knew could work.

Furthermore - can you imagine having to use a large robotic arm over all that airbag material? It'd be a nightmare. Compare MPF's science payload in kg's - and compare it to that of Phoenix..... the question answers itself.

Doug

The question will really only be answered after the field testing -- ie. when Phoenix and MSL land safely or as scrap. Remember that most people thought airbags were daft when the Pathfinder team proposed them, and again when the MER team scaled them up considerably. Both teams went through hell to prove the concept. Now they are just a footnote even though they've been shown to reduce risk in EDL.

That said, I'm cautiously optimistic that they will successfully land the heaviest payload ever on Mars. But if they don't, it's MER 2.0! Wouldn't it be absolutely amazing to send another MER every launch window with evolved power, instrumentation and mobility and reduced mass each time? It works beautifully, so reuse it to death!

If you're evolving power, instruments, movility and cutting mass - you're not reusing anymore

Doug

I can imagine Beagle 2 ( again ). The airbags were not supposed to be deflated after landing, the lander just had to separate itself. Overall, all instruments connected to the PAW seemed very attractive to me.

Beagle 2 was designed to detach from the airbags entirely and then drop to the ground. I was refering to the concept of landing Phoenix with MER/MPF style airbags and then trying to use its arm to reach over them.

Doug

I'd like to raise another question. Smart Landing! NASA shoudn't give up the idea of a lander that can avoid dangerous objects. We know that Spirit and Opportunity used somethink like that ( Mars Descent imager + selective rocket firing ).

No - MER had no means to avoid hazards. The decent imaging motion estimation system ( dimes ) was there to calculate the speed of the spacecraft across the terrain so as to calculate which TIRS (Transverse Impulse Rockets) to fire when firing the RAD motors to tilt the vehicle over and cancel out as much of the wind-induced speed across the terrain.

It was not there to identify hazards and thus avoid them

Doug

Obstacle avoidance is difficult since the lander has only its own vertical imagery to work with. Assuming lighting conditions were appropriate it could perhaps use shadows in the descent images to identify large boulders and laser ranging to identify slopes that were too steep to land on. I think with present technology it is too much to shoot for.

If the EDL system could target a much tighter landing ellipse on the surface, perhaps the lander could be loaded with a half metre scale elevation model which it could then refer to when picking a safe place to land. Still I would think that must be years away from practical use.

Really good idea, Mark, but you're right...probably years away. It takes a LONG time just to get CPUs, memories, etc. qualified for airborne use, much less for space, and you're talking about some fairly formidable RT processing capability here. Still, it's definitely within the realm of the possible, even probable.

Actually, using airbags is good for any experiments where hydrazine and other rocket exhaust end-products would contaminate the ground and make it more difficult to find what you're looking for in the soils around the lander. As it is, Phoenix data will have to be adjusted somewhat to filter out the observed effects of rocket exhaust on the soils that will be studied.

The odd part of this equation is that you want soils undisturbed by rocket exhaust for your heavier landers, while you're not nearly as concerned about the issue if you're just deploying things like seismometers and weather stations. So, in that regard, rocket landers are more appropriate for netlander-style small stations, while airbags are more suited to larger payloads. Unfortunately, the physics and engineering of the landing systems are exactly the reverse, with airbags more suited to small landers and rocket-assisted landings more suited for large, complex landers.

I think the solution is basically to make large landers which would benefit from undisturbed soils at least somewhat mobile. The problem there is that you spend an awful lot of your mass budget making your probe mobile, which means you have less mass than you'd like for experiments.

-the other Doug

The good stuff Phoenix is after is 10's of CM's deep....not only should the exhause be easy to identify and filter out - but it's not going to make it that far underground.

Doug

My theory is any movie that deals with Mars has a 95% chance of being a bad movie... There are definately a large number of problems with this one, more than most of them.

My idea about the airbag landing was much different. A crew can't survive an airbag landing, but could this be used as a backup system during unmanned landing? For example, Phoenix:

1. Parachute deployment- nominal.
2. Heat shield separation - nominal.
3. Separation of the lander from the aeroshel - nominal.
4. Ignition of the hydrazine engines - not nominal then switching to a backup system. Ejection of the landing legs+ engines then airbag inflating...

The main problem will be all that weight.

Well - the mass of the airbags would rule out every iota of instrumentation, communications hardware...everything.

It doesn't even begin to make sense.

Better to invest the time, money, volume in making the primary landing system reliable. Hell - if your airbags would work for a phoenix like lander - why take the thrusters and hydrazine at all? If your backup is going to be perfectly reliable when called upon - then why have the primary?

Better is the enemy of good enough.

Doug