
The Art of Aerobraking 86
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.""
"Uncertain atmosphere" (Score:1)
=> use retro Thrust.
Hell, I just won a position as Nasa's Chief Engineer 8)
Re:"Uncertain atmosphere" (Score:3, Interesting)
The danger lies in using aerobraking to rid yourself of all your velocity. If you use if to get rid of a nice portion of it and then thrust your way to a complete stop (relatively speaking, of course), you get the use of the atmosphere with less risk.
Aerocapture (Score:5, Informative)
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.
Re:Aerocapture (Score:1)
I guess what I mean is how difficult would it be to build a craft capable of smashing directly into Mars's atmosphere (perpendicular to suface normal) and slowing down that way? I mean certainly the heat stress would be tremendous, but certainly there's solutions to that...
So the plan is that it smashes down in there, then once it realizes it's slow enough, it can deploy a series of parachutes to slow it down even further...
Aerosmash (Score:5, Informative)
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 [nasa.gov] website for more details.
Re:Aerosmash (Score:1)
Re:Aerocapture (Score:1)
Re:Aerocapture (Score:1)
Didn't Mars Climate Orbiter already demonstrate aerocapture? (Apologies to the JPL folks..)
Re:Aerocapture (Score:2)
Original Story Link (Score:2)
Now if only the Martian defense force does not get the probe.
;-)
No Fear (Score:1)
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.
Re:No Fear (Score:1)
Re:In Thrust We Trust (Score:1)
Come on, we are talking about orbital insertion here.
I thought that nobody was having sex on the ISS yet???
Nonsense (Score:1)
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
Re:Nonsense (Score:2, Insightful)
To add to this, there is an upgrade in the works. Several parts of the orbiter are being upgraded. The Avionics system is one of those. They've already put new displays and computer hardware in the cockpit and after the avionics is upgraded in a few years, it will be "up-to-date".
I agree that we need the money and public support that we had in the Space Race days of Mercury through Apollo. Unfortunately the public sees no reason for this. Back then we had the Cold War to fuel our need to advance in space technology. Now most people could care less. I don't think any wars in the next 10 years will show a demand for a TIE-fighter, unfortunately.
As for the space station
Nitpicking, I know... (Score:4, Informative)
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.
Due diligence and sleep dep (Score:2)
Ahhh, thanks (Score:1)
For those who want to see it in action. (Score:2, Interesting)
Aerobraking vs. Propulsion Braking (Score:3, Interesting)
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.
Re:Aerobraking vs. Propulsion Braking (Score:2, Informative)
They did. It was called Mars Pathfinder. It bounced around on those big airbags for a while, and after it came to rest sequentially deflated them so the payload ended the right way up.
What's a 'sustainable' atmosphere?
... That was the idea. (Score:1)
Re:Aerobraking vs. Propulsion Braking (Score:2, Informative)
BlackGriffen
Re:Aerobraking vs. Propulsion Braking (Score:3, Informative)
For atmospheric entry however parachutes alone are not enough. Mars's atmosphere is 1000 times less dense than Earths. What parachutes are used for is to give a huge reduction in speed, from about 900 MP to about 160 MPH. A parachute that does this weighs about 10 KG. A parachute that would bring pathfinder to a survivable landing would have a 250 ft diameter and weigh 420 kg, more than the lander itself! It's much better to slow down some with a parachute then use retro rockets in one form or another.
-Mishra
Re:Aerobraking vs. Propulsion Braking (Score:3, Informative)
Bzzzt! Thanks for playing. I wish I had your confidence in NASA's management. Unfortunately, instead of emulating successful missions such as Mars Pathfinder, NASA is planning to spread the model for a failed mission (Mars 98) throughout the agency.
Mars Pathfinder was managed and built in-house by JPL -- this was the lander / rover mission which succeeded wildly (albeit with modest goals) in 1997.
Mars 98 was the combined missions of Mars Climate Orbiter, Mars Polar Lander, and the experimental Deep Space 2 impact samplers. The loss of the two primary spacecraft was attributed to poor coordination between JPL and the contractor who built them (Lockheed Martin Astronautics).
Yet, the "plan" being advanced to contain the massive cost overruns on Space Station, is based on outsourcing as much work as possible. Hmm. I'm not saying that outsourcing is always a bad thing, but NASA had better tell the taxpayers what's going to be different in the new formula.
Here's NASA's "Commercialization" plan:
http://www.spaceref.com/news/viewsr.html?pid=3730 [spaceref.com]
Aerobraking and probe intelligence... (Score:5, Informative)
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
Intel has some of those (Score:3, Informative)
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)
Re:Aerobraking and probe intelligence... (Score:1)
See the RAD750 CPU and embedded computer family at:
BAE Systems [baesystems.com].
It's true that you probably don't want to use off the shelf CPUs in deep space (though many of them will do acceptably well; the typical deep space radiation environment is not so bad, if you don't fly during high solar flare times and can put up with a few resets from time to time). But there are plenty of space-rated components for those who know where to look and have the $$$. It's not bleeding edge, but it's not that far back either.
Re:Aerobraking and probe intelligence... (Score:5, Interesting)
You mean like Deep Space 1 [nasa.gov]? Or Clementine [navy.mil]? Yep, it's being done.
(3 minutes later, and atmosphere unexpectedly thickens) SP: oh no! Quick, recalculate! rocket, give me a 2 second burn then turn 43 degress for a 1 second burn!
Oop, doesn't work that way. Orbital mechanics is funny until you wrap your head around it. To change the perigee, you have to burn at the apogee. Once you're in the atmosphere, there's bugger all you can do about it until the next time around. (Well, unless you're carrying gobs of fuel, and if you can do that, the screw this aerobraking stuff.)
Of course, you can make the probe autonomously adjust the next pass based on the results of the current one. But I wouldn't want to even try until we have at least one more probe's worth of data on exactly how to model all this.
And in response to the AC who thinks that rad-hard processors aren't up to this, all I have to say is HAW! Go look up what processing power the guidance computer on Apollo 11 had, and marvel at how much you can do when you're not spending cycles drawing aqua-colored drop shadows. I could make a useful aerobraking auto-adjust system with an RTX-2010 and half a meg of RAM. (That's an 8 MHz Forth processor, folks.) If that's not enough for you, Lockheed-Martin is selling rad-hard 250 MHz PowerPC 750 boards for only two arms and a leg.
Re:Aerobraking and probe intelligence... (Score:1)
Re:...probe intelligence... (Score:3, Funny)
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")
Re:Aerobraking and probe intelligence... (Score:1)
Re:Aerobraking and probe intelligence... (Score:2)
Inertial navigation's not as accurate as GPS, but it'll do in a pinch.
Re:Aerobraking and probe intelligence... (Score:2, Informative)
Light-minutes and light-years measure distance, not time.
Re:Aerobraking and probe intelligence... (Score:1)
Light-minutes and light-years measure distance, not time.
I'm sure he knows that. If you are 10 light-minutes away from me, it will take 10 minutes for your radio signal to get to me, since radio waves propagate around the speed of light.
Re:Aerobraking and probe intelligence... (Score:2, Interesting)
The difficulty is in getting a sensor that can tell the controller what the air density is. The obvious way to do this would be with an accelerometer but these are expensive and don't really work well enough anyway (with current technology). Wing-like control surfaces would also help -- but these add weight and cost.
Aerobraking and Aerocapture hold a lot of promise as most of the fuel carried by these probes is used to go into orbit at Mars (or your favorite celestial body).
Re:Aerobraking and probe intelligence... (Score:1)
Well, no, actually. Accelerometers are not terribly expensive, and work just fine. Silicon Designs [silicondesigns.com], for instance sells rad-hard ones. You also want to watch the temperature on various parts of the spacecraft. Temperature sensors are even cheaper than accelerometers.
Measuring what you need to measure is not hard, nor are the calculations. All we need is a better understanding of what controls the density at the top of the atmosphere. Once we have that, you can bet autonomous aerobraking will be as common as cherry pez.
Re:Aerobraking and probe intelligence... (Score:2)
The situation you described is called "adaptive guidance". Consider the problem of launching the Shuttle into orbit. A human is typically not involved in the loop at any point except to monitor systems and choose an abort mode if a failure should arise (and even then, the MC's are the ones who usually make the call). The algorithm(s) are not for sissies, they involve nested intregals and all sorts of fun stuff.
During reentry (which is a similar problem to aerobraking) the humans are only involved in the loop during the final approach stage, and that is not even neccessary -- it's just good to have a human already in the loop, so they can better detect and respond to a problem. And yes, you can measure pressure at Mach 25, but what do you do with it? How do you know what the pressure is one second later, when you've traveled 7 km?
The reason that the Shuttle can perform reliabily is that we have a very exact model of the Earth's atmosphere, including variations due to solar flares, and the time of day. Our model of Mars is not quite as refined, and the accuracy is more critical-- just a velocity different of a few 1/10's of km/s can make the difference between aerocapture, burning up, or spinning off into space.
"In thrust we trust..." (Score:2)
Ahem, posted since yesterday (Score:2, Offtopic)
Must we always discuss everything twice? [slashdot.org]
Re:Ahem, posted since yesterday (Score:1)
What really gets me is I get posted in "science" and this gets front page.
What's the difference?!?!
And Mr. On Crack Moderator. Read both articles before placing this "off-topic". It should be modded up as "Informative"!
Atmosphere Cheap - Thrust Expensive (Score:2, Interesting)
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.
Re:Atmosphere Cheap - Thrust Expensive (Score:2)
Why lug around a fairly large tank of propellents with all its associated weight penalties and possible risk that restarting the rocket motor could damage the spacecraft? I believe that a quite plausible theory why the 1993 Mars Observer disappeared was that when they tried to restart the onboard rockets to slow the spacecraft down there was a propellent explosion that may have destroyed the spacecraft.
Besides, the Mars Global Surveyor showed that aerobraking can be done safely.
Come on, think about it.... (Score:1)
Will the Martians allow this one? (Score:1)
just a couple typos (Score:1)
Should be Mars Climate Orbiter and Mars Polar Lander, if I recall correctly...
Brakes? (Score:1)
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?
Re:Brakes? (Score:1)
Given our recent track record, "smacking into the surface of the planet at 4000 kph" is about all our probes have done anyways. Might as well build for it ;)
Re:Brakes? (Score:2)
Some extra information... (Score:3, Informative)
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
Aerobraking better than "Trust in Thrust" (Score:2, Interesting)
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.