Phoenix Launching

[EricRobodox]

It launch on time at UTC 5:26. Nice clean launch, very cool to watch.

[Roger]

Stay up to watch? I usually get up at 5:00 am (east coast time), so I didn't have to do an all-nighter. I turned on NASA-TV Saturday morning to see if there was any news about the next Shuttle launch (Wednesday eve), and here they were launching a different rocket!

Any reason on not using the airbag landing for Phoenix? When I first saw that I was <raised eyebrow>, but now it looks . Imagine that for a ride at Six Flags!

There certainly seems a lot of Mars projects. Keep it up!

[EricRobodox]

Its not really a rover, so there is no need for it not to be careful about a drive system. Airbags would be useful for that. But if its like my mission, Mars Science Laboratory, it may be too heavy for airbags to work. And thrusters allow it to land wherever it would like, rather than less predictability from the bouncing of the airbags. Many reasons probably why they did a thruster landing. Clean launch though, very cool.

[Roger]

When I saw yesterday's Astronomy Pic o' the Day (http://antwrp.gsfc.nasa.gov/apod/ap070808.html), it said it wasn't a rover, and I had my "Ah ha!" moment why no airbags. But all your reasons (and many more) make sense. After all, you guys had years to decide all this.

I seem to be lucky this week. First seeing Phoenix go up. Last night I got home just in time to see the shuttle launch on broadcast TV -- didn't even have time to pull out my laptop to get it on NASA-TV. But NASA-TV was a couple of minutes behind "live", so I got to see most of it again!

What did you do for your 2009 mission, Eric? Anything interesting?

[dlavery]

Originally Posted by EricRobodox

Its not really a rover, so there is no need for it not to be careful about a drive system. Airbags would be useful for that. But if its like my mission, Mars Science Laboratory, it may be too heavy for airbags to work. And thrusters allow it to land wherever it would like, rather than less predictability from the bouncing of the airbags. Many reasons probably why they did a thruster landing. Clean launch though, very cool.

Actually, the rationale for the use of a propulsive landing system rather than an airbag system for Phoenix is pretty straightforward. It has nothing to do with whether or not their is a rover on board. Phoenix was originally proposed as the first flight project for the Mars Scout program, which was envisioned as a series of (relatively) low-cost flight projects for Mars exploration. To keep the proposed project under the cost cap (yes, space flight projects have cost limits imposed on them too!), the spacecraft was designed to re-use several hardware items scavenged from prior spacecraft. For example, the arm on the Phoenix lander is the flight spare from the 1999 Mars Polar Lander. The main structure and landing system for Phoenix is actually the hardware originally built for the 2001 Mars Surveyor Lander project, which was cancelled before it ever flew. So Phoenix is using a propulsive landing system because they are using the hardware from the 2001 lander, and that is the method that the earlier mission was designed to use. But why wasn't the 2001 mission designed to use airbags instead of propulsion?

The answer to that is revealed when you think about the timelines involved. Airbags were used successfully for the first time on the Mars Pathfinder lander, which touched down on Mars on July 4, 1997. Up until that time, airbags were an untested, unproven technology. The Mars Surveyor Lander mission was intended to launch in April of 2001. But that meant that the spacecraft was actually being designed in the mid-1990's. Rather than potentially risk the 2001 mission on a technology that no one had seen work, in 1995-1996 the designers chose to stick with a propulsive landing system similar to that used on prior missions like the Viking 1 and Viking 2 landers. By the time airbags were shown to actually work in 1997, the construction of the 2001 lander was so far along that it would have been much more expensive to stop the project and re-design for the use of airbags than to just finish building what had already been designed.

-dave

p.s. This was not the only place that unused 2001 Lander project hardware showed up on other missions. The "Athena" science package that was orginally slated as the primary payload of the lander was brought forward and became the primary payload carried aboard the Spirit and Opportunity rovers launched in 2003.

[EricRobodox]

Wow, thanks dave. Learn more every day. I just assumed the positioning thing because i went to a JPL seminar on SecondLife, but they had mentioned about situations about the airbag system that if in a certain position, not sure which but assuming in a hole of some sort, could not open correctly. So i thought maybe they were going to land it with thrusters to steer clear of holes and obsticles.

roger, i said it wasn't a rover. Mars Science Laboratory, Mars Exploration Rovers, and Sojourn/Pathfinder are the only NASA rover missions to mars currently. I think, i may need some correction, Beagle is as well, but that is mainly European Space Agency's, and that was not successful.

[Roger]

Well it didn't sink in the first time about the rovers. I was just thinking that if you wanted it at a certain small target, dropping a big bouncy ball wasn't the ideal method if your payload didn't have wheels to move around. Or maybe the terrain was a little too pointy rocks to bounce an airbag on. But then again, you guys have had many years and many projects to figure out details like this. I just wonder (not in a criticizing way) about the reasoning behind some of the decisions. And as dave explained, sometimes the reason comes from a place or time far away and not obvious.

NASA must have this eclectic collection of leftovers and never-finisheds. I have this image of this old grizzly guy with a huge garage/junkyard in the back lot of NASA, saying, "Rocket to Mars, eh? Let's see, I think I got something you'd like back here. Almost rode it back in the last century. You need some arms probes, too? I got one over here -- still in the box...."

[EricRobodox]

lol, there was a career fair while i was working there were i got to talk to people from all over JPL, and he was talking about how the missions are chosen very selectively and that tons of missions concepts dont make it, even with hours upon hours upon hours.... upon hours of research and design have gone into the proposal. Then on top of it, there are also some major dates that after approved need to be planned and worked out, like design and other things that are somewhat over my head. I think for MSL, the major like meeting was done March or May, i know it was just before i came in, and MSL has been approved since i think 2001 or 2003. one of those. Little tired at the moment, and cant think too straight. If Dave knows more about it, im sure he wouldnt mind explaining a bit.

[Roger]

And besides Joe or Jill Scientist having to go up the bureaucratic chain with their proposal, there's the problem of making sure the planets are aligned so they can get there.

[EricRobodox]

Mars every two years. Thats why there are launch windows. But yes, planet allignment is*most always*, and thats an assumption, to be in the proposal. Thats why they are proposed so early, so they can hit it. Keep in mind ATLO (Assemble, Test, and Launch Operations), which is when they assemble the flight hardware, takes place about a year or two before launch (at least it is for MSL), compared to the entire mission being started sometimes 10 years before launch.