Why is Opportunity lasting so long?

[Frida Space]

I think they don't really need vehicles that last more than 4 years, after that amount of time they are due for technological upgrades and new instrumentation, time for a new mission. NASA really could plop out a new mars mission every year and within 20 years have a sizable exploratory coverage of mars without ever stepping foot on mars.

That's true, and it's exactly what they're doing for the new 2020 rover: they're already thinking of the rover after that!

From SpaceNews:

Once thought of as a sample-caching mission, NASA now plans for Mars 2020 to extract several surface samples from each region it visits and leave them on the ground for a future rover to cache, Ken Farley, Mars 2020 project scientist at NASA’s Jet Propulsion Laboratory, told the Mars Exploration Program Analysis Group (MEPAG) during a Feb. 24 meeting in Pasadena, California.

Not sure I really like the idea though.

[BagelRabbit]

The reason that the Opportunity rover is lasting so long is that it's a simple system that doesn't require much power, coupled with an incredibly robust design that can take a serious beating and keep on going, coupled with the fact that Mars is the best planet in the Solar system to send rovers to, coupled with the careful efforts of mission planners and a fair deal of luck. Spirit would have lasted for a similar amount of time, too, except for the fact that it got stuck in a tough spot and couldn't get enough sunlight.

As for the solar panels, Martian dust is largely attracted to them by static cling; astronauts on the Moon experienced the same phenomenon. If there was a way to negate the static charge, the panels would almost always be free of dust, as a slight breeze would lift it into the air. The spaces between panels would be dusty, but that wouldn't really be a problem (unless it caused a short-circuit, which is unlikely.)

[PB666]

That's true, and it's exactly what they're doing for the new 2020 rover: they're already thinking of the rover after that!

From SpaceNews:

Not sure I really like the idea though.

Sure but when you have down time on one mission you can flip the switch on one of your old rovers and see if you can push it another 500 meters, and do some more sampling.

Im glad to see they have Kepler back on line, crippled but still functioning.

[Camacha]

You know a great solution to this problem? A goddamn CPU fan mounted near the front of the solar panels.

Seriously, NASA, is it so hard to get rid of a little dust?

That is actually a lot more complicated than you make it seem. Not only would a CPU fan also be full of dust and rapidly become useless, but the Martian atmosphere is a lot thinner than ours too. Blowing stuff away is a lot different than it would be here.

Also, dust only became a problem after the rovers survived a lot longer than expected. I am quite sure dust was not the main reason the rovers had minimum life span of 90 days - you have to absolutely guarantee operation for the specified period of time, deal with unknown factors and probably have a safety factor built in. Combine that with Mars being relatively benign to rovers and there is a good chance your device will last quite a bit longer.

[tater]

A quad copter faces the same issues, it'd have to be much larger than the actual rover I'd bet.

[Camacha]

A quad copter faces the same issues, it'd have to be much larger than the actual rover I'd bet.

That is true, any vehicle that attempts aerodynamic interaction faces difficulties. It is one of the reasons parachutes on Mars are somewhat hairy. We have trouble testing them here, so any flight will be a test flight, although quad copters might be tested in a large vacuum chamber, one that is possibly filled with the same gasses at the Martian atmosphere has.

[GoSlash27]

A Martian tweener found it and adopted it as a pet. He cleans it's panels when we're not paying attention

Best,

-Slashy

[cptdavep]

What I can't figure out is why they have sent a completely different rover in Curiosity, and spent billions on the project when they could have probably sent lots of the proven Spirit/Opportunity design robots for the same money, with less risk, and explored lots of locations, maybe with varied instruments on the rovers. Seems a no brainer to me that when you make something so good you make full use of it!

[Yukon0009]

Because it's just designed to be plain tough.

[RainDreamer]

Makes me wonder how well will the fancy new helicopter drone being designed for Mars will work. It doesn't look so tough.

[K^2]

That is true, any vehicle that attempts aerodynamic interaction faces difficulties. It is one of the reasons parachutes on Mars are somewhat hairy. We have trouble testing them here, so any flight will be a test flight, although quad copters might be tested in a large vacuum chamber, one that is possibly filled with the same gasses at the Martian atmosphere has.

NASA has some

. That should be enough even for some good 'chute data. There's also an option of dropping things off high altitude balloons. You can get one high enough up to simulate lower Martian atmosphere.

[Camacha]

NASA has some

. That should be enough even for some good 'chute data. There's also an option of dropping things off high altitude balloons. You can get one high enough up to simulate lower Martian atmosphere.

They can get some decent data, but one of the problems actually was that they could not properly test parachutes, especially at the speeds they encounter when doing a landing. I do not think I can find it right now, but NASA engineers described the landing as being the test flight.

[Ralathon]

What I can't figure out is why they have sent a completely different rover in Curiosity, and spent billions on the project when they could have probably sent lots of the proven Spirit/Opportunity design robots for the same money, with less risk, and explored lots of locations, maybe with varied instruments on the rovers. Seems a no brainer to me that when you make something so good you make full use of it!

Because the Opportunity design does not have a lot of spare power to spend on science. It's pretty pointless to pepper the martian surface in machines that simply can't run the experiments we want to run. Opportunity had about 0.6 kwh a day while the Curiosity has 2.5 kwh.

Weight is also a problem. Some scientific experiments are just too heavy for the Mars Exploration Rover design. The EDL sequence would fail with them on board.

[sgt_flyer]

There's an easier way to test out hypersonic parachute deceleration in thin atmosphere than vacuum chambers (creating hypersonic winds in vacuum chambers is extremely costly and can only be sustained for a few seconds) - you simply launch your test system in earth upper atmosphere, and deploy the test parachute at high speeds when you reach the correct entry angle and atmospheric pressure to mimic the conditions of mars atmosphere.

Nasa recently tested an inflatable reentry heat shield with a sounding rocket as a booster

http://www.nasa.gov/directorates/spacetech/game_changing_development/HIAD/irve3-success.html#.VP2QFJZPfCQ

[PB666]

Because the Opportunity design does not have a lot of spare power to spend on science. It's pretty pointless to pepper the martian surface in machines that simply can't run the experiments we want to run. Opportunity had about 0.6 kwh a day while the Curiosity has 2.5 kwh.

Weight is also a problem. Some scientific experiments are just too heavy for the Mars Exploration Rover design. The EDL sequence would fail with them on board.

But we now know we can target a landing site, so that if you one thing and you want to study it with heavier equipment, simply drop a robotized lab on top of it.

The problem of slowing stuff in mars upper atmosphere is a matter of transport costs, you could make a lightweight frame in space that, using drogue chutes and larger chutes you really could slow things down. (remember that drag is the square of speed)

So lets say that mars is 1% of earths atmosphere, that means that for an earth sized chute it will be going 10 times as fast when it hits the ground. (instead of 6 it is going 60 m/s)

If you double the area you get it down to 0.707 * 60

If you quadruble you get it down to 0.5 * 60 = 30

if you octuple you get it down to .35 * 60

if you increase 16 times you get it down to .25 * 60 = 15

if you increase 64 times you get it down to .125 * 60 = 7.5

if you increase it 128 times you get it down to 0.08825 * 60 = 5.30 M/S

If your goal is to return a rocket from mars this is a relative good solution, you don't need to go down to 5.3 m/s you can simple get it down to 20m/s and fire your rockets close to the ground to land (its relatively easy when you only have to correst for a small dV on landing)

So the investment really is building such a frame in earth orbit and then spiriting it off to Mars.

So here is one of my space port suggestions,

Create a medium earth orbit thin metal frame building with sliding doors that can be used to assemble bulky stuff (Extend the life of the space station another 40 years)

Instead of docking a rocket draft it into the facitility close the doors, disassemble the construction materials, and bungi them to the side of the building.

You could even create such a facilitiy on Phobos and use robots

(Although the problem with Phobos, Mars, Diemos is getting the power to do the job. Literally the side of the building could be solar.

[Sampa]

Well, I suppose that, relatively, at the time of Opportunity's launch, NASA was not exactly pinching pennies and could afford to build more reliable vehicles. Also, I think a simple fact of irony exists. The more we learn about an area, the more questions we have! We already have a vehicle on site that still functions so, let's use it while we still have it!

[-Velocity-]

Also, dust only became a problem after the rovers survived a lot longer than expected. I am quite sure dust was not the main reason the rovers had minimum life span of 90 days - you have to absolutely guarantee operation for the specified period of time, deal with unknown factors and probably have a safety factor built in. Combine that with Mars being relatively benign to rovers and there is a good chance your device will last quite a bit longer.

Incorrect, here is a quote from a paper on the subject-

Although the MER mission was given a life expectancy of

only 90 Martian days (sols), this was not due to any

particular limitations in the rover hardware. Rather, it was

tied to anticipated loss in array power due to dust

accumulation on the panels (based on information from

the short lived Pathfinder Lander and rover), and

additional sunlight loss from the encroaching winter

season.

P. M. Stella and J. A. Herman, “The Mars surface environment and solar array performance,†in Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE, 2010, pp. 002631–002635.

The main reason the rovers have lasted so long on PV power is the unexpected cleaning events. In a nutshell, the same forces that lift dust into the air (wind) also cleans the rover's panels. When it gets really dusty, it also tends to clean the dust away too, and it ends up being a sort of self-limiting process, though things can still get bad, so both rovers also had a bit of luck. I have a power point presentation on it, but I don't know how I could share it with you guys.

Edited March 9, 2015 by |Velocity|

[-Velocity-]

Here's some plots demonstrating the paradoxical link between increased dust in the air and decreased dust on the MER solar panels. Both of the plots are from the same source.

Spirit-

Opportunity-

Both images-

P. M. Stella and J. A. Herman, “The Mars surface environment and solar array performance,†in Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE, 2010, pp. 002631–002635.

The "dust factor" is a measure of the amount of sunlight that makes it through the dust layer on the solar cells, so the higher the dust factor, the less dust (the maximum value is 1.0, of course, where 0% of sunlight is blocked by dust accumulation on the solar cells).

Tau is an expotential term that's related to the amount of direct sunlight that makes it to the surface. Basically, the rovers would take a picture of the Sun, and its brightness would be used to compute the atmospheric extinction tau value according to the formula

I = Io*exp(-tau)

where

I = observed intensity of sun

Io = known actual intensity, no extinction

ANYWAY, observe the cyclical pattern of tau values. At a periodic interval, tau tends increase, typically with three spikes. This increase corresponds to the powerful summer hemisphere summer, where the high eccentricity of Mars' orbit brings it closest to the Sun simultaneously to the southern hemisphere experiencing its summer season. This leads to a lot of dust storms.

Notice that the dust factor (inversely proportional to the amount of dust covering the arrays) tends to be the highest during this stormy, dusty season on Mars. This is especially true for Spirit. This is because, like I said, the winds that bring dust into the air also clean the dust off the panels. The amount of dust cleaning by these winds was unexpected, and this is really what allowed the rovers to last so long.

- - - Updated - - -

Finally, notice the huge jumps in dust factor- sometimes it will increase all of sudden. These are known as "cleaning events". We believe that the MERs get struck by large, random gusts of wind- perhaps even dust devils, and these gusts remove a huge amount of the dust accumulation all at once. These also tend to happen during the stormy, dusty season on Mars, but are a bit more random.

Here's a before and after image of a rover's sundial. I believe this is from the big the cleaning event Spirit experienced during its first Martian year (see the plot for MER-A above).

Edited March 9, 2015 by |Velocity|

[Streetwind]

Little tidbit on long-lasting Opportunity:

Right now it is 128 meters short of its historic "marathon distance" milestone of 42.2km total driving distance... and not driving.

Why is it not driving? Because it has, once again, discovered something previously unseen. The composition of some rocks on the site doesn't match anything found on Mars so far. They've stopped to investigate.