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The Art of Aerobraking
gizmo_mathboy writes: "Yahoo! Dailynews has the following Space.com article about the risk of using aerobraking for orbital insertion of spacecraft versus the certainty of using conventional propulsion systems. This is all explained in terms of the Mars Global Surveyor craft that is expected to do its orbital insertion on October 23. Skip the wimpy aerobraking and as a prophead trapped in a code monkey's job I say, "In Thrust We Trust.""
So what, you cannot aerobrake if thin atmosphere...
=> use retro Thrust.
Hell, I just won a position as Nasa's Chief Engineer 8)
It takes 40+ muscles to frown, but only four to extend your arm and bitchslap the motherfucker
Hmmm... In Thrust We Trust... That's the name of a flick on the Hot Network this month.
I think they should take the risk of Aerobraking. Hell, so what if it fails the first time? It's not like anybody's going to die and I'm sure sure they have the money to throw away.
You die too easily.
Actually, it's the Mars Oddessy craft that's about to perform aerobraking, the Global Surveyor has been in Mars orbit for several years now.
No, I don't want a free iPod
A really nice demonstration of this can be seen in the movie 2010 (the sequel to the famous 2001). The Russian spacecraft uses this technique to slow down for an orbit around Jupiter. It's really fun to watch. If the science only partially intrigues you, then watch the movie just because it has John Lithgow. I like that actor more than Keanu Reeves.
"It's the little touches that make a future solid enough to be destroyed" --William S. Bourroughs
You mean the Mars Odyssey spacecraft, of course...
I am sure in the interest of reducing size, reducing weight, reducing cost, and increasing the amount of available instrument and sensory device space onboard an interplanetary craft which is designed to land on an alien planet within a certain *limited* budget, exploring as many alternative kinds of landings mechanisms is well withing the realm of understandable and highly saught after.
Packing a couple of large parachutes into a space craft for landing on a planet with a sustainable atmosphere would make a lot of sense if the means of adding an entire rocket/fuel powered landing/propulsion system onto the same craft would not produce greater yield/results within the intended mission/budget. Why not design a craft which could always 'right' itself regardless of how it is situated after it lands with a parachute type landing? That would/should not be a very difficult task given the amount of incredible talent that is at NASA's disposal.
As a *very* sincere and heartfelt sidenote...Policy usually destroys or f*cks up NASA missions. That is a *certain* gaurantee...NOT the entire staff of Ph.D. Physists and Engineers working on the projects. It always makes me sad/unhappy when people blame NASA engineers for NASA's recent terrible public mistakes. Blame policy, politics, and administration (be it impossible deadlines, mismanagement, etc.) for NASA's recent unfortunate public image. Things are getting better every day and by the minute and all it will take is just one immensely and incredibly perfect mission for NASA's public image to be returned to it's former 'moon landing' era confidence. Thank You for listening. Please support NASA and it's mission to keeping dreams and imagination alive despite the rest of the world's problems.
Using aerobraking to rid yourself of 'all your velocity' (interplanetery velocity, relative to the orbital motion of the target planet) is called aerocapture. This has never been attempted before, and would require prescise atmospheric targetting (to within a few kms), precise details of the atmospheric density parameters, and perfect understanding of the spacecraft's atmospheric behaviour, all on the first, and only 'deep' pass through the atmosphere. Since we are 'burning off' all our interplanetery velocity in one go, the heat load would be quite extreme, probably needing a dedicated heat shield, which could be discarded after the aerocapture pass. Of course, the spacecraft wouldn't need an Mars orbital insertion (MOI) rocket engine, and the ton or so of fuel that would go with it. (A smaller rocket burn however would be required 1/2 an orbit after the 'deep' aerocapture pass, to raise the spacecraft enough so it wouldn't pass through the atmosphere a second time). Once aerocapture has been achieved, and the spacecraft had been checked out (and allowed to cool down!), a gentler aerobraking phase can then be used over time to reduce the orbital velocity of the space craft, and lower the resulting eliptical capture orbit into a circular one suitable for science studies.
It has been proposed to use areocapture for some of the later mars orbiter missions, but it was deemed too risky, particularly after Mars Surveyor98's areobraking phase showed how unpredictable the Martian upper atmosphere really is.
If you remember the film 2010 (I think), the Russian exploration ship used areocapture at Jupiter, by inflating huge baluttes (balloons) around the craft and plowing through Jupiter's atmosphere.
-- We don't understand software, and sometimes we don't understand hardware, but we can *see* the blinking lights
No, I'm not going to talk about V-ger or anything like that.
The article mentions that one of the major problems with aerobraking is the fluctuation in density of the admosphere causes problems with calculations for the aerobraking. That got me to thinking...
Now, recently, we've started to build the landers with a reasonable amount of autonomous intelligence, so they can cope with some problems without requiring instruction. However, from all that I've read, all the space-borne probes we've send are dumb as a rock: that is, they can't do anything that Mission Control doesn't tell them to. They're a true remote-controlled vehicle.
The problem with this approach is the time lag between Earth and wherever they are (which is measured in light-minutes). I realize that adding some sort of intelligent processing to a probe causes an additional weight to be carried (and power consumed), but for christ sakes, I can get a Lego Mindstorms to run around my livingroom by itself; one would hope that we might be able to build a semi-autonomous space probe.
Basically, we should be able to build something that does this (MC=Mission Control, SP=Space Probe):
Basically, what I'm suggesting is that we break the mentality of requiring absolute control over the probe at all times, and allow them a degree of adaptability and flexibility by providing them with some reasonable programming. That's no happening now. And as the maneuvers we attempt grow in complexity, we're going to find it almost impossible to completely pre-calculate everything. If we keep trying, we're going to fail.
Adaptable and intelligent semi-autonomous probes are the long-term solution.
-Erik
There are always four sides to every story: your side, their side, the truth, and what really happened.
Hmm. You mean trust like they did with a previous Mars probe that accidentally reentered (may it rest in its pieces) due to a miscalculation over the size of the thruster?
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Must we always discuss everything twice?
They devellop hardened cpu for space exploration.
I seem to remember Hubble is using *hum* 486 dx2-66 with cosmic ray shield for stability calculation...(those got replaced after they fixed the lens the first time, they got an upgrade to Pentium Pro, I think)
Don't know about your Mindstorm CPU, but that should be twice its power...
BTW If it can find its way in the Living Room, did you manage to get it to open the fridge yet ? 8)
It takes 40+ muscles to frown, but only four to extend your arm and bitchslap the motherfucker
MC: Bomb #20, please return to the bomb bay.
SP: But I received the drop order.
MC: The drop order was in error. Please return to the bomb bay.
SP: OK, but this is the last time...
...
Captain: Talk to the bomb... Teach it phenomenology...
...
SP: In the beginning there was darkness, and me...
(Rusty memories of AI hardware in "Dark Star")
The living have better things to do than to continue hating the dead.
No, they DON'T have the money to throw away. The US space program (the best in the world) has serious money troubles. They are attempting to hold together a serious program by going for the cheaper, lighter technologies (such as this aerobraking) which is fine and good, but the fact remains that the program has been basically gutted ever since the moon flights.
/. needs that!
This is deeply sad, in my opinion. What we really need is a shuttle Mark II (that first one is really just a prototype.. a good prototype, but it really needs to get past version 1.1.9.). We need a _real_ space station. We need a program that lets us start mining asteroids, so that we don't have to keep lifting every expensive gram of water up to orbit. And, of course, we need a really good Sh*t Recycler (tm). Heck, even
Economically, aerobraking is definitely the way to go. Putting large amounts of propellant on board would make the mission more expensive, or take the place of instruments, radio gear, computers, etc.
Until we get really advanced propulsion technologies that are both powererful and economical (high thrust, high specific impulse), we're going to need to use methods like this.
"Open the pod by doors, Hal" > "I'm afraid I can't do that, Dave" sudo "Open the pod bay doors, Hal" > alright
...as a prophead trapped in a code monkey's job...
I prefer to be balled a "Keyboard Cowboy"
YeeHaw!!!
--
Does anyone remember
Pinging dailynews-a.snv.yahoo.com [216.136.131.80] with 32 bytes of data.
216.136.131.80
Eek! It would probably not be possible to enter and land through mars atmosphere 'perpendicularly'. For 'entry' purposes, assume mars atmosphere to be 125Km high. The spacecraft is travelling at interplanetery velocity, say 7.5Km per sec. If we decide not to slow down, we will hit the surface in 17 seconds with a *big* bang.
The time is too short to run the entry sequence (jetesson heatshield, deploy parachutes, fire retros etc)
The deceleration G forces required to slow down in the limited time would be massive, (>100 Gs, causing structural engineering design issues)
The total integrated heat load on the heatshield would be the same, but the peak loads would be much higher (up to half a gigawatt. Thats a lot of asbestos)
And since you are going 'straight down', once you jetesson your heat shield (and its stored thermal energy), you will probably land on it a few seconds later and melt.
The ideal solution (as demonstrated by mars pathfinder) is to come in at an shallow angle of about 15 degrees, and in this case the whole entry sequence takes a good few minutes, the peak deceleration is about 20Gs and the peak heat load is about 100Megawatts.
See the Mars PathfinderEntry Descent and Landing website for more details.
-- We don't understand software, and sometimes we don't understand hardware, but we can *see* the blinking lights
Thrust breaking is not going to be around for long. Why? Because it isn't acceptable. Too difficult? Yes it isn't easy to do, but then again getting a ship to mars isn't easy either but we did that. This is just the next hurdel. Most of the fuel is spent escaping the earth, the last thing you want to do is add to the total mass that must be accelerated. Not to mention that when a thrust reducing craft reaches mars its total mass is far greater than a craft that uses aerobreaking. Did I mention that crafts that use aerobreaks can get there faster, while using less fuel? AND... If you were to ever plan a return trip from mars, the amount of fuel you would need if you relied on thrust to induce your -delta V, would be FAR too much. The air density CHANGES? No!! You're KIDDING!! Next thing your going to tell me is that the atmosphere is constantly changing, almost like WIND! Gimme a break. If you REALLY want to understand this topic, and the different proposed methods for reaching mars with a crew and returning them to earth, then you should go checkout/buy The Case For Mars. The solution is not giant, zillion dollar monster ships, but small, light, quick craft.
That rad-hard processors aren't up to this sort of thing.
Don't forget, the Martians have an excellent track record of taking out our spacecraft. I wonder if they'll let this one into orbit, or take it out the way they did the Mars Observer in 92 or the Russian Phobos missions.
Now if only the Martian defense force does not get the probe.
;-)
"It is a greater offense to steal men's labor, than their clothes"
The twin failures of the Martian Chemical Orbiter and the Martian Polar Lander in 1999 have ...
Should be Mars Climate Orbiter and Mars Polar Lander, if I recall correctly...
I read this as Aero-bra-king.
Hmmm... In Thrust We Trust... That's the name of a flick on the Hot Network this month.
Come on, we are talking about orbital insertion here.
I thought that nobody was having sex on the ISS yet???
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
Jesus, I was thinking "that thing's been at Mars since I was in high school! It's STILL not done aerobraking?" Well, good to know then that aerobraking is just sort of slow, rather than ludicrously slow.
"The question of whether a computer can think is no more interesting than that of whether a submarine can swim" -EWD
We don't need no steenking brakes!
Why bother with braking at all? Why not just design the thing to survive smacking into the surface of the planet at 4,000 kph or whatever it's going to be doing when it gets there?
Just be sure to wear the gold uniform when you beam down -- you know what happens when you wear the red one.
2001 was an astounding, thought-provoking masterpiece about man and his relationship with the universe.
2010 was just another Hollywood space flick compete with Sound in Space(tm).
The aerobraking sequence was kinda neat 'though, in spite of the "explanation for morons in the audience through letter to the spouse" beforehand.
I wouldn't mind a snuggle with a Russian babe whilst going through aerobraking either.
Other fun stuff to watch for:
A.C. Clarke feeding pigeons in front of the White House.
A.C. Clarke as President of U.S. on Time cover.
Stanely Kubrick as President of U.S.S.R on the same Time cover.
Just a comment: I'm reading some comments from people saying that this is the first time aerobraking has been used. This is not true. Mars Global Surveyor (http://mars.jpl.nasa.gov/mgs/) used aerobraking to do it's orbital insertion several years ago. This is said in the article, so I'm surprised that people are saying that's it's a new technique. In any case, MGS's aerobraking phase was extremely successful. There is of course this fear of the atmosphere suddenly thickening, but this wouldn't happen in a matter of seconds, it would take quite awhile, enough time for the spacecraft to respond.
The story says that the MGS had some problems with aerobraking. Yes, it had some problems, and they said it took longer than it should have, which it did, but the way that they did it was much safer than direct orbital insertion with conventional propulsion systems. The primary source of the problems was (and I know this from following its news DURING it's aerobraking phase) that they didn't want to hurt an already damaged solar panel, so they were being very conservative because if they lost that panel, the mission was over. They normally could have easily handled the inconsistencies, but that in combination with the solar panel problem made them reevaluate some things:
To make sure the panel would be alright, they needed the pressure on the panel to be less that 0.2 N/m^2. They could only do this by extending the aerobraking phase. The major reason for breaking it up into two phases was because there would be a solar conjunction in June, 1998 in which we would not be able to talk to MGS for awhile. Thus we got it out of aerobraking mode before we were going to lose communication. It began phase two so late because a major part of the mission was to map Mars, and to do this required the spacecraft to be in certain places at certain times. To achieve this, they needed to wait awhile before restarting aerobraking.
There was not a fear of "crashing" the spacecraft here - they wanted to keep that solar panel intact, so they lengthened the aerobraking phase, which made them rearrange the mission slightly. It really wasn't a big deal.
Also, "labor-intensive" is a bit of a stretch - the orbits at the beginning of the first aerobraking phase were on the order of a couple days, and only a fraction of that time was spent going through the atmosphere, which gave them a very large amount of time to figure out where the spacecraft was and where it was heading. The phase 2 aerobraking orbit (much easier than phase 1) to begin with was about 12 hours. It definitely wasn't a scramble. They also fail to mention that a lot of science was done both during and in between the aerobraking phases - it wasn't a wasted year.
Also, it seems to me that now that we have the information (density data, etc.) from the MGS aerobraking, the Odyssey aerobraking predictions will be much better. In addition, if the MGS predicted atmospheric densities and such were so far off for the MGS mission, and MGS still survived, then Odyssey will do fine. It's just a matter of being conservative.
Let's remember that the spacecraft doesn't just go flying into the atmosphere, it gets itself into a very large, very elliptical, "rough" orbit, after which it begins aerobraking to lower the orbit and slows itself down. I'm sure somewhere on the MGS website you can see how it lowered its orbit with each pass, making it more circular. It's really slow, and from what I've seen from MGS, quite safe procedure, assuming you're careful.
I don't know if this helps anyone out. But really, the aerobraking phase isn't all that dangerous, and using the MGS as an example of how difficult it is is definitely a mistake.
JoeRobe
The best way to predict the future is to invent it.
As it turned out, the Pathfinder came to the end of it's roll, pretty much perfectly vertical, so only a simple deflation sequence was needed.
Aerobraking is an elegant solution, making possible missions that aren't otherwise possible. Applying the lessons learned from Mars Global Surveyor, just make sure your structural design is sound, and go about your aerobraking conservatively and patiently.
.00000001% chance (or whatever level of risk you're willing to assume) of overheating or overstressing the spacecraft on any given pass.
In other words, you do the statistics and you just dip far enough into the atmosphere that there is only a
Maybe someday thrust will be so cheap we don't need to spend weeks in an aerobraking phase, but until then, I hope we get very good at it.
That that is is that that that that is not is not.
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.By using a modified Hohmann orbital transfer it would be possible to[[[[Secret]]] that the obital curves match.
If NASA didn't make such fools of us in front of the Cavemen, maybe none of this stuff would have happened. If we had a base on the moon they wouldn't have concieved of any of this.
I knew I should do a quadruple check of anything I submit/post after 3am. Not to mention the fact it was a dupe (but I can sorta blame Michael for that. Ain't due diligence a bithc? ;-)
AC 1: It's already there...
AC 2: Well, aren't you a fucking wit
AC 3: I love your mom and your sister too.