# NASA counts down to nuclear tank invasion of Mars

It's T-40 days unti NASA's nuclear powered Curiosity rover arrives at Mars and commences re-entry and descent to the surface beneath its hover-rocket sky crane lander - and the space mission's engineers are biting their nails. It's not the first time the space agency has talked about "seven minutes of terror". Pretty much …

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#### Excuse my ignorance...

...but won't a 21 foot tether be too short from 20 metres up?

#### Re: Excuse my ignorance...

Well shucks, isn't 21 bigger than 20?

When will NASA enter the 21 century and adopt rational units??

#### Re: Excuse my ignorance...

All measurement systems are totally man-made and a foot is no less rational than a metre.

The only rational unit might be to measure everything in Planck lengths!

#### Re: Excuse my ignorance...

I hope they don't forget to descend the final ~7 metres or they'll do a 'nukular pillinger'!

#### Re: Excuse my ignorance...

Er, no. Not when the thing then descends until the rover's wheels hit the dirt some 21-and-some feet below it isn't.

UoM is unimportant too. As long as tether length < distance to ground at deployment, everything's fine. No need for any exactitudality[1] on this one.

[1] While I'm being unusually positive and friendly toward the yanks, I might as well go the extra mile and use the language.

#### Re: Excuse my ignorance...

I suspect the engineer has just mentally converted 7M into 21' because its easier for him to visualise.

#### Re: Excuse my ignorance...

Of course the foot is no less rational than the metre. After all, it's trivial for anyone to convert feet into, oh, let's say, miles (after you guess which kind of mile we're talking about). So, how many miles in 457 feet?

On the other hand, converting say 457 metres into kilometres requires the wholly counterintuitive process of shifting the decimal point a three places to the left.

#### Re: Excuse my ignorance...

Planck lengths? You'd spend half your development time just writing out the numbers.

Pity they cannot land near Spirit or Opportunity, so they could film the descent.

Awesome project, I will have my fingers crossed those 7 minutes of terror

#### MER rovers recording MSL descent

Pity they cannot land near Spirit or Opportunity, so they could film the descent.,,

Yeah, that would be pretty cool, but even if they were able to precisely target the MSL landing to a point within sight of Opportunity's cameras, it'd probably still be a toss-up as to whether or not the Opportunity cameras would be able to catch it. There'd be all kinds of timing issues, I'm sure. Maybe -- maybe -- Opportunity might be able to catch MSL incoming if its entry/descent flight path carried it over the area where it's currently working.

Still, we do have that spectacular shot that the MRO camera got of the Phoenix lander's descent under its parachute -- as I recall, a wide, sweeping panorama of a large crater with Phoenix, still in its aeroshell, with its 'chute fully blossoming above it in the relatively near distance, backdropped by the floor of the crater. The foto was at a high enough resolution that when you zoomed in to 1:1, you could see the parachute lines extending down to the lander. Gorgeous. Still, if I remember, it was a case of MRO simply being in the right place at the right time.

#### Feet and pounds and meters ...

No wonder they screw things up! A 21 foot tether 20m from the surface? You'd have thought rocket scientists would at least keep to consistent measurement units, wouldn't you?

#### How long...

...before the damned "martian curse" kicks in and we lose this vehicle, too?

#### Re: How long...

Yeah they are flying in the face of the odds with this one, expect strange flashes from Mars, as they retaliate to our dirty bombing of the Martian surface.

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#### Re: How long...

...before the damned "martian curse" kicks in and we lose this vehicle, too?

As I recall -- at least lately -- the Martian Curse seems to have only affected Russian missions, and in many of those cases, it was due to sloppy programming or engineering. Some of the early US missions had that problem, too, but by the time of the Viking missions, JPL pretty much had it going on.

Oddly enough, though, now that you mention it, the Russians have had extraordinarily good luck with Venus missions.

#### Re: How long...

After a good run of missions, the Americans lost Mars Observer in 1992, Climate Orbiter in 1998 and Polar Lander / Deep Space 2 in 1999. The UK then lost Beagle 2 in 2003. Since then its been nothing but successes apart from - oh dear - the Russians again with Fobos-Grunt.

#### Re: How long...

@Symon: "The chances of anything coming from Mars are a million to one." Presumably tongue in cheek - so I won't bother to say it again.

#### Re: How long...

@ Mike Flugennock: "Oddly enough, though, now that you mention it, the Russians have had extraordinarily good luck with Venus missions."

Only goes to show: Make love not war!

#### Re: How long...

@ Mike Flugennock: "Oddly enough, though, now that you mention it, the Russians have had extraordinarily good luck with Venus missions."

Only goes to show: Make love not war!

Whoa, nice one! Well done!

Just upvoted.

#### More metric/imperial confusion?

So the team measuring the altitude were working in metric (20 metres) and the team buying the rope were working in feet (21 feet) - will they never standardise???

#### Re: More metric/imperial confusion?

We are standardized. The engineers work in units your typical American understands and the scientists work in that Celestial Goofy Shit system (CGS for short).

#### Re: More metric/imperial confusion?

Hey, Tom, CGS went out decades ago - it's MKS now.

#### Computers are good for this:

"We've got literally seven minutes to get from the top of the atmosphere to the surface of Mars, going from 13,000 miles an hour to zero in perfect sequence, perfect choreography, perfect timing,"

#### Re: Computers are good for this:

Compuers are good for it if you ask the right questions. As phrased, the answer is simple: Just drop the thing.

He's omitted the need to do the last few cm very slowly...

#### Re: Computers are good for this:

"We've got literally seven minutes to get from the top of the atmosphere to the surface of Mars, going from 13,000 miles an hour to zero in perfect sequence, perfect choreography, perfect timing,"

Actually sounds that like the judging on 'Strictly Come Dancing'

#### Re: Computers are good for this:

Drop anything from 13,000 miles up, and it will end at zero velocity!

Seven!

#### NASA mixing units again on Mars. What could possibly go wrong...

NASA engineers mixing imperial and metric measures in one video. Miles, kilometres? Feet, metres? Hope they get it right this time.

http://articles.cnn.com/1999-09-30/tech/9909_30_mars.metric.02_1_climate-orbiter-spacecraft-team-metric-system?_s=PM:TECH

"...arrives at Mars and commences re-entry..."

<pedant>

Surely "...commences entry..", unless it's been there before?

</pedant>

You got there before me :-)

#### Idiots view

I'm not keen on all these high speed manoeuvres. I'd prefer much more that retro rockets, parachutes, and air brakes were used in the upper atmosphere, and then they can deploy a large balloon, for a gentle descent to the surface. I really hope that it all works. For me space exploration is the only thing that excites me about technology these days. Here on earth the "bad monkey's" are still killing one another over trivial things, monkey hives (cities) are overcrowded, resources are running out, or so the greedy monkeys tell us. It is just a shame that all the greedy control freaky monkeys ensure that trillions are spent on means to kill other monkeys rather than really solve the problems of the day.

Perhaps this scenario is our only hope.

"It is the result of reasoned engineering thought, but it still looks crazy."

Well, sure, but...it's so crazy, it just might work!

They added the tether specifically to make it a one-in-a-million shot.

You can tell it's a government-funded project. They're using reasoned engineers to design their ridiculous crazy shit, rather than saving money by just getting unemployable lunatics to do it.

#### All THREE American rovers used sky cranes w/ teathers...

Fact check. sojourner and the long-lived rovers ALL used these cranes with teathers. The difference here is that there is no air-bag encapsulating the rover-module. It is not without risk, but it is an incremental improvement from the MELs...

#### crazy?

Well, sure, but...it's so crazy, it just might work!

As it's often been pointed out here, the method being used for MSL is really no crazier than the idea of encasing your landers in bouncy balloons and just letting it fall in, bounce, and roll to a stop. As I recall, the airbag landing system used on Pathfinder and MER also contained thousands of parts that all had to work just right, controlled by millions of lines of code that all had to execute just right in a computer that had to work just right.

Same with Apollo, waaaaay back in the day; there were a mind-numbingly huge number of complex hardware and software systems that all had to work just right in order to get the crew to the moon and back.

The real pucker factor is that nobody on Earth will know what is happening before it is all over.

#### "We've got literally seven minutes to get from the top of the atmosphere to the surface of Mars"

Doesn't gravity take care of most of this? I mean I don't think it's a challenge getting from the top of the atmosphere to the surface, nor going from 13,000 mph to 0, although I grant you the last bit can be tricky if you want to use anything afterwards...

#### Stop!

"... going from 13,000 miles an hour to zero ..."

Well slowing from 13,000 mph to zero is really not that difficult, when heading downwards.

The trick is to achieve it without resorting to lithobraking.

#### Re: Stop!

I just laughed out loud at the mention of lithobraking, earning me a few odd looks at the cafe. Well done, good sir.

#### Re: Stop!

Isn't that lithobreaking especially when it goes wrong...

#### Does it have a miniature repair team?

For the other rover?

#### 21 or 20

Whilst NASA may well be guilty of mixing their units, I'm not sure the difference between 21 feet and 20 metres actually matters. Depends on what they meant by lowering it slowly to the surface. If they want to hover at 20 metres and use the wire to lower it all the way to the surface, that's an issue if it's 21 feet long. However, if they want to lower the rover on it's 21 foot wire when at 20 metres and then gradually drop the lander to deposit the rover, that's fine. The lander will be at 21 feet when the rover touches down. Without knowing which one is their idea, it's difficult to say if their feet/metre issue will present a problem.

Whilst a very interesting way of delivering the package and certainly more entertaining than other more conventional methods, I'm not sure why they've chosen this method. We've got a lot more experience of dropping a lander on reto-rockets to touch down than trying to hover them. Then, the rover could run off the top. Not sure what the issue was with that, but dangling a rover under the lander seems unduly complex. Given the difficulties of carrying loads under helicopters on earth, this seems silly.

Alos hope there are no aliens around when the lander detaches the rover and fires off to its destruction. Not sure they would appreciate a lander hitting them.

#### last minute check

I seriously urge NASA to use these last 40 days to re-check which part of the whole shebang is expecting its input in fractions of imperial units. Considering the thing was built and operated by engineers such as the one interviewed here, there's high probability of a non-metric bug stuck somewhere in the middle. Hopefully, it's not a 21 ft rope gently dropping the buggy from 20 m above surface...

#### Then there is the "invited guests"

Down at JPL in Pasadena (California, not Texas) and an auxiliary site a city or two away, LOADS of people are going to visit. All sorts of politicos and "distinguished visitors" of every stripe. Having a brother in law in charge of working the antennas (the deep space network, Hi Wayne!) didn't get me a seat at all, so I have to watch it on a computer as the Satellite service (DirecTV) doesn't have it on the default channel list (curse, curse).

The weird thing is that by the time the telemetry gets back to Earth, the whole thing will have done its deed (pass or fail). When we get word of it entering Mars (little) atmosphere, it will all be over. Hopefully the Mars orbiter will snap a pic like it did on the last lander. At 8:30 we'll get nice pictures and all will be well! I'll then go back to bed.

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#### Uh Oh, hope the bankers keep their noses out.....

Bit worried that RBS/NatWest may have a hand in the software development - even if the Lander has a soft touchdown it'll be at least 2 weeks before we hear Will.I.Am's composition

#### Re: Uh Oh, hope the bankers keep their noses out.....

The last 7 minutes are outsourced to India. Expect disaster when some inexperienced operator deletes the tether. ;)

#### Thunderbirds Are Go!

"500,000 lines of cod3"

"1000 times thinner"

I've got all my fingers crossed for this one.

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