2 Science Questions

[whiterafter]

Hi! I have just 2 questions.

1. How does NASA calculate encounters? I am not sure how they would be able to tell their probe would get an encounter and know the orbital parameters, etc. I would expect there to be misses in space but there aren't many missed encounters.

2. With probes running way over their project length, does NASA start to extend primary mission plans? Opportunity lasted 10 years over their planned 90 days and I wonder how much science could have been done had they expected a longer running life.

Thanks

Whiterafter

[Superfluous J]

1. They do what we do, essentially. They have very smart people with very sophisticated computers and fantastic information gathering abilities, so they know exactly where everything important is and where it's going, and what burns to do to make the probe go where they want so it'll be in the right place at the right time to intersect its target.

2. I secretly believe that NASA has a full 10-year plan for every "90 day" mission they've ever made. They can't tell the public about this, though, because if in year 5 the probe breaks down the press will be all over them about how they failed halfway through. If it breaks in year 5 of a 90 day mission, though, they look super frugal and resourceful keeping the little guy running for that long.

[Nibb31]

1- They use computers. However, they typically work in reverse to what we do in KSP. Instead of launching the rocket and figuring out how to get to the destination from there, they determine where they want to put the probe, the various dV options to put it there, and work their way back to launch.

2- The extended mission objectives are vaguely outlined before the mission. It's not secret, but the details are decided on an "as we go" basis, depending on where they are, what they found, and whatever resources (time, money, power, propellant) are left.

[Scotius]

Planning a 5-year mission takes much more work and money than planning of 1-year mission. And all that work can go BOOM 5 seconds after launch. So i guess NASA plans for short, "barebone" mission at first, and extends the plan when everything goes right and mission is considered safe to put more man hours into.

[Cirocco]

science and engineering rant time!

number 1 has been answered already so I won't re-iterate what has been said already.

As for your second question: it's a combination of several factors.

For one, it's impossible to say how long a mission will last because so much is unknown and there are waaaaaaaaaaay too many variables which cannot be foreseen, especially when attempting things that have never been attempted before. Spaceflight is truly cutting-edge: there is so much we don't know and almost every mission is doing somethign that has never been done before. At the time, spirit and opportunity were some of the largest rovers ever sent to mars, and not a lot of rovers had gone before them. Scientists had theories and ideas about the difficulties it would encounter, but there wasn't a lot of real tried and tested information, so NASA is pessimistic and only gives a timeline they're reasonably confident about.

Secondly, spaceflight is an industry where quality is of the absolute utmost importance. Things get way overdesigned with several back-up systems and failsafes. If these failsafes are not needed, they can be salvaged or re-purposed to extend mission lifespan, but there's no way to know that on launch. Improvisation is a big part of these missions because the amount of resources to resolve problems is extremely limited. Again, in the case of mars rovers it isn't uncommon to use certain instruments for uses they were never initially designed for, but you use them anyway because it's all you have.

thirdly: rovers (and lots of other space instrumentation) are specifically designed not to have an "off" switch. You never know if someone might press it by accident. And especially for rovers with solar panels, it's completely impossible to know how long those solar panels will work. Will they be covered in dust? Will the topography allow for hills so we can angle the panels towards the sun? Will there be fortouitous gusts of wind that clea the panels? Will there be a dustsorm that sompletely covers the panels and kills the mission 2 days in? No one knows. So again, you assume worst case.

You also wondered how much extra science could have been done if longer mission profiles were anticipated? Probably not that much. During those ten years, opportunity has been doing everything it can with the instruments it has on board. It doesn't matter if they planned it initially or not, opportunity has been giving us information non-stop for those ten years. If you want to do more in-depth science, you need better instruments. Those are heavier, meaning more money required, bigger scope, bigger mission, etc... Basically you'd end up planning a really big mission without any prior experience, not even knowing if all those heavy and expensive experiments you sent up will even result in good data. This is an example of "scope creep", which is the bane of many projects in any industry.

In essence, you shouldn't send a curiosity rover which weighs as much as a small car when you know next to nothing about the risks. Start small, learn from small missions, scale up. That's what spirit and opportunity and their predecessors were for.

As frustrating as it can be, it's never a good idea to go with high-risk missions in something as expensive and critical as space exploration. Slow and steady wins the race as it has been said.

[LordFerret]

Hi! I have just 2 questions.

1. How does NASA calculate encounters? I am not sure how they would be able to tell their probe would get an encounter and know the orbital parameters, etc. I would expect there to be misses in space but there aren't many missed encounters.

2. With probes running way over their project length, does NASA start to extend primary mission plans? Opportunity lasted 10 years over their planned 90 days and I wonder how much science could have been done had they expected a longer running life.

Thanks

Whiterafter

In case you did not know, there are services available at NASA where you can ask their scientists questions such as these directly - and receive legitimate authoritative answers!

http://science.nasa.gov/ask-a-scientist/

Now, if you'd like to play with some software for calculations (pretty much the real deal) you can check these out.

http://www.nasa.gov/centers/johnson/copernicus/

http://open.nasa.gov/blog/2011/07/28/space-mission-design-for-everyone/

[Mazon Del]

2. With probes running way over their project length, does NASA start to extend primary mission plans? Opportunity lasted 10 years over their planned 90 days and I wonder how much science could have been done had they expected a longer running life.

There was a chart on Wikipedia a few years ago that has since been taken down that showed something very interesting. It had date along the bottom, and "Mean time before equipment failure" for Curiosity's equipment along the left axis, and cost of Curiosity's equipment on the right axis. The data was showing that Curiosity's equipment was set for the first failures to begin a couple years after the end of the first intended period of operation on Mars. The project was also pretty on budget at this time. Then there is a data point on the date line that was a year or two after Spirit and Opportunity's landing, where they just kept getting funding for mission extensions. Suddenly the cost of Curiosity's equipment begins to rise fairly dramatically, but so did the "Mean time before equipment failure".

If the chart is real, then it was indicating that they chose to accept cost overruns on the hardware in order to give the equipment extra lifespan on the assumption that they would pretty much always be able to secure funding to keep running the radio communications to direct it. It is easier to ask for a couple $100K to run a system already in place, than it is to ask for a couple billion for a new launch.

If I remember right, the projected lifespan of the equipment is now set such that as the power output from Curiosity's RTG falls, it will eventually reach the point where even though the power can only activate one science package at a time, something like 90% of the science packages should still be operable.

[pincushionman]

In actuality, the dynamics of the solar system's orbits are well-understood, and not that hard to solve, especially after 50 years of doing it. You just need time and precision. And as long as you're "close enough," you have plenty of time for correction burns as you go. The hard part is getting hardware that's rugged, reliable, precise, and light enough to do the (relatively straightforward) things the mission plan calls for. It's not only a harder problem, it involves way more people to make mistakes. When was the last tome you heard of a mission failing because of "we missed," rather than "something broke," except early on when the programs were still getting their feet under them?