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NASA tests supersonic parachute, to help us land on Mars

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Supersonic parachutes have a limited number of uses.

Supersonic parachutes designed to deploy at pressures 1/160 of Sea Level even more so.

Historically the big ones are

1) Nuclear weapons deployment from supersonic aircraft

2) Entry to planetary or lunar atmospheres (IE Mars, Titan, Venus, Jupiter).

IIRC the last article I read on the subject was penned by someone at Sandia labs, who don't have a keen interest in planetary exploration. Which may explain the coyness on design.

Exciting idea as Mars atmosphere is so thin you need huge sub sonic 'chutes

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But how...

do you test a parachute designed for very low atmospheric density on Earth? Would opening the chute at x miles up accurately replicate the conditions?

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Re: But how...

Yes, choose the correct altitude and speed and conditions are near enough you can get the right data.

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Re: But how...

Would opening the chute at x miles up accurately replicate the conditions?

Yes, and it would do so better than a wind tunnel. NASA has had difficulties testing Martian parachute designs in wind tunnels because of difficulties matching Martian conditions.

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Re: But how...

Part of why SpaceX is so confident they can land on Mars without a parachute is the testing they've done in high Earth's atmosphere.

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Coat

Premature release?

Seems the parachute went off a bit sooner than they wanted to.

Let's not be too hard on NASA, it happens to the best sometimes. All that excitement probably got to it a little bit.

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Re: Premature release?

" ... it happens to the best sometimes."

All these comments and nothing ejaculation related yet. Sometimes I despair of the comentards.

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Alien

Descent?

"The Reg worries about the sharp descent that seems not to follow the hoped-for flight profile."

Agreed that it's not the hoped-for profile, but that 'sharp descent' is in the velocity graph... ie it slowed down very quickly. That seems to be pretty much what they were hoping for, just that the 'chute deployed too soon.

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Re: Descent?

If the chute deployed too soon, does that mean it was further up than it should have been (in thinner atmosphere?), and that the good test results are actually excellent?

Or does it mean it deployed before rocket reached full height (in thicker atmosphere) and therefore teh good results are to be taken with a pinch of salt?

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Boffin

Re: Descent?

It looks like it opened at a lower speed than planned, it's hard to read the scale (and why was the graph drawn from right to left?) but I think it deployed at about 180 ft/s (what's wrong with SI units for rocket science?) instead of 200ish.

It's not the worst graph I've ever seen, but whoever made it has made some questionable choices in units, orientation and choice of data to display.

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Re: Descent?

If it deployed too soon, then it also deployed at the wrong height with the wrong atmospheric density.

If so, then the test only shows that the Earth's atmosphere at a lower altitude is denser than Mars' and parachutes are much more efficient. But I think we already knew that.

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Boffin

Re: Descent?

Not necessarily Just Enough. It very much depends on the flight Profile of the rocket. It's normal during launch, to turn off the engines once your airborne and cruise until you're at a higher altitude and then turn the engines back on. The reason to do this is to get the additional velocity you Need only after you've escaped the thicker parts of the atmosphere (this is in fact necessary as if the air density is too high you will burn up if you're going too fast).

So if the rocket was already at the right height, it might have only needed the boost to get it to the right velocity. If it fired before that boost, your velocity is lower than planned but your height/atmospheric density could be right.

This is of course speculation on my part. I'm at work and cant access Videos so cant check out what's shown in the article.

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Pint

wrong atmospheric density

Sorry it's Friday and it put me in mind of this....

"Indicate the way to my abode...I'm fatigued and I want to rest my cranium hic..oh I had a little beverage 60 minutes ago and it's gone straight to the UPPER PORTIONS OF MY BRAIN..wherever I perambulate hic..over land or sea or atmospheric density hicx..you'll always hear me crooning hic ..this lullaby indicate the way to my aboooooooooode" I thank you hic. PP

I will get my coat but only 1 icon for this.. Happy weekend Commentariat.

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Severe kinetic landing?

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DJO

Severe kinetic landing?

Yes, normally followed by an unscheduled rapid disassembly.

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Nominative determinism

Given how often nominative determinism comes true, I do wonder about the logic of having a facility called Wallops

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Windows

Re: Nominative determinism

@Hans N-B

Quite some time ago a friend of the family had an Irish Water Spaniel who was always happy to see anyone, and thus always had much tail activity - the dog was called Wallops, since that was what he did, walloping everything and everyone with his tail. I somehow get the feeling that naming the *launch* facility for rocket testing Wallops is actually quite appropriate. Although I'm quite sure that there is another (cough) tale to the origin of the site name.

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Re: Nominative determinism

There is a Wallops Wood (and farm) in the UK so its probably just a name transfer (like Boston, Cambridge, Paris etc etc ).

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Re: Nominative determinism

Per Wikipedia it's named after John Wallops. So.. family name.

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Supersonic problems

Is use of a parachute at supersonic speeds difficult because it's at a speed greater than the speed of sound (with attendant complexities of airflow, shockwaves, etc) or just because it's very fast?

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Boffin

Re: Supersonic problems

It's a big ball of Problems from my understanding. Aerodynamics is a big Problem, since stability in the Environment is not a common Feature (turbulence at supersonic speeds is a b&tch!). Material science is also a killer - things travelling at supersonic speeds get very very hot when you try to slow them down with drag. Thats why landers always come with a heat shield, it's the heat shields job to burn away during the descent so that the spacecraft doesnt have to. Determining height and velocity etc behind a shockwave also isnt easy, as it messes with your pressure calculations/Radar telemetry/etc., so determining when to release the parachute is a problem (see the Mars lander Schiaparelli)

I'm sure there are a tonne of other complexities involved, but those three are a good starting Point! ;)

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Boffin

Re: Supersonic problems

It's related to the fact that it's greater than the speed of sound. Not through causality though.

Basically, sound goes at that speed because that's the speed that air molecules bump into each other nicely. To go faster than that you have to move the air around you faster than it is comfortable going.

Think of it like driving through a traffic jam vs free-flowing traffic.

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Anonymous Coward

They're looking at this now?

So somebody says "Hey! Lets develop a parachute suitable for the Martian atmosphere and the mission!". Wouldn't it have been more sensible, for, ooh, the ESA to have thought about that some while back?

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Windows

Re: They're looking at this now?

@AC I get the idea that they started thinking about it *quite* some time ago. There's a bunch of used parachutes scattered all over the martian surface that seem to attest to that.

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Re: They're looking at this now?

Aren't the parachutes needed for the projected larger payloads to be delivered to Mars?

For the smaller ones they've been using sub-sonic parachutes and bouncing balls; and of course the sky-crane for Curiosity.

Or am I way off beam?

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Anonymous Coward

Re: They're looking at this now?

From what I read ESA had done work on parachutes etc and as had a project to send a Mars orbiter follwoed 2 pr 3 years later by a lander they decided the incremental cost of adding a lander to the first mission to test the landing mechanisms was a good idea ... and as it turned out it showed there were some issues and you would hope the experience of this would give a much better chance of a corect landing on what wa alwyas the real lander project

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Re: They're looking at this now?

Off beam? Perhaps they could use my un-attractor beam. Or leer as its called by some.

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Re: They're looking at this now?

"used parachutes scattered all over the martian surface"

Couldn't get this out of my mind.

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Re: They're looking at this now?

"Aren't the parachutes needed for the projected larger payloads to be delivered to Mars?"

Yes, the ones already used were for much smaller payloads.

This mission is much heavier than anything that's gone before and needs more aerobraking as a result. That means a bigger parachute deployed higher up, at higher speeds.

Almost all missions have used parachutes at some point in the descent, just not necessarily all the way to the ground, and preferably not to negative altitudes.

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Alien

These things must be heavy or have massive ripstop stitching.

I am curious as the weight of the chute that is required to slow the object down. Does the weight become exponentially heavier as the weight of the it is slowing down becomes heavier? Also, is the parachute just used to slow the capsule down so less fuel has to be carried for a soft landing or is the aim to use the supersonic arresting device all the way to Martian Firma?

Huge space interest but as you can see very little technical knowledge or ability.

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"I am curious as the weight of the chute that is required to slow the object down. "

Depends on the heat load.

IIRC normal parachute nylon is about 70g/m^2 but high temperature materials are more around 700g/m^2 (the HIAD demonstrator was "loosely" a parachute type material).

But Mars Sea Level is 1/160 that of Earth Sea Level, so what would be a baking temperature for an Earth entry could be quite survivable with just Nylon, even though you're slamming into it at very high speed.

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