Questions about real space programs

[Tazin]

After playing around with KSP for months, i have become interested in the real world of space exploration. This led me to a few interesting questions that google could surely answer, but i rather have a KSP fan's take on them:

-Is aerobraking used IRL? i realize there are not many interstellar flights coming into earth, but for example when a ship comes from moon orbit, does it burn retrograde to orbit earth? or does it aerobrake in upper atmosphere? is it a reliable manouver, or is it a risky last resort?

-What is earth's atmosphere real limit? that marvelous 70km point that separates being on earth from being on space? Since there isn't really a hard point where atmosphere just stops, how far away can atmosphere be traced?

- What are earth's real escape velocity, and orbital velocity at minimum altitude?

- Are ships in real space always under the influence of a celestial body, don't they ever just float there? i imagine it can't happen in the solar system, but in interstellar space i guess you are not really "orbiting" or "escaping" anything, right?

- What is ISS's altitude? do they change it often or is it stationary? who "runs" the ISS and makes decisions like changing it's orbit and stuff?

- Have astronauts done stupid things? i remember watching Armaggedon, and the token russian guy at the ISS had a bottle of vodka stashed away, i thought "wow, alcohol must REALLY be banned on the ISS" but then again, people up there get bored so i imagine they do stupid things too, like trying to smuggle something, people getting into fights and arguments, breaking stuff? engaging in baby making or other sexual activities?

- If a crime is comitted in the ISS, whose jurisdiction is it? has that ever happened?

- What's the real cost of launching an oribital mission, like an ISS supply run? what about the cost of landing on the moon?

[NovaSilisko]

1. Real aerobraking is a very slow, progressive process, only dipping in a tiny bit of the atmosphere at a time. Going in deeper requires more heat shielding and thus more mass. It was done very successfully by the Mars Reconnaissance Orbiter, as one example. Coming in from an escape trajectory and slowing yourself into an orbit using the atmosphere isn't called aerobraking, also. It's called "Aerocapture", which has never been performed due to the mass issues I mentioned before. In the case of the Apollo missions, there were no retroburns before entering the atmosphere. They just entered directly, keeping the G-forces down by offsetting the capsule's center of mass slightly, which allowed it to enter at a slight angle, thus producing lift - the capsule actually briefly ascended again after entering the atmosphere, in a very slight skip trajectory.

("Interstellar flights"? Did you mean interplanetary?)

2. There is no "limit". It just fades out to nothing very slowly, but even at the altitude of the ISS and beyond you get subtle atmospheric drag. It's almost impossible to tell a minimum limit. Around 100 km to 120 km (maybe a little low), though, is about the limit where you can make a few orbits, depending on the aerodynamic characteristics of your spacecraft.

3. Around 11 km/s and 7.6 km/s respectively.

4. Yes. In interstellar space you are still affected by the gentle gravity of the stars around you, and the supermassive black hole in the galactic center which all stars orbit around. There's no such thing as a hard-limit Sphere of Influence like you get in KSP. You're always affected by all bodies. Technically, everything in the universe is exerting a gravitational pull on you, even if it's absolutely ludicrously infinitesimally tiny.

5. Around 400 km or so, but it changes a little bit every so often for various reasons (it frequently requires reboosting to compensate for atmospheric drag, as well as occurances such as adjusting it to make it easier for a vehicle to rendezvous. The whole altitude of it was kept lower for the sake of the shuttle, and after the shuttle was retired it was raised) It's generally an agreement between NASA and Roscosmos to maneuver the station, as the manuevering will be carried out by Russian Progress vehicles. The European ATV used to do reboosts, but that was retired.

6. Possibly. Walter Schirra on Apollo 9 7 (thanks harbingerdawn) had some conflicts with flight controllers over his unwillingness to carry out parts of the flight plan due to the fact he was generally miserable after developing a cold. John Young and Gus Grissom smuggled a corn-beef sandwich to orbit on their Gemini flight, which the controllers were incredibly mad about. Sexual activity? Not as far as anyone knows... it would be pretty difficult to hide. There was one astronaut who kidnapped somebody, I think, but that was on the ground. I forget her name.

7. It hasn't ever happened, but IIRC the jurisdiction depends on what country's module you're in.

8. Almost impossible to say. Depends on the value of the cargo, which rocket and spacecraft, etc. The shuttle was about 1.5 billion dollars per launch. Apollo, actually, was fairly similar, only a bit higher. (adjusted for inflation, not sure if my memory is correct on the last fact though)

Edited August 19, 2015 by NovaSilisko

[NFUN]

This might be better placed in the Science Labs.

-There are zero interstellar flights coming into Earth, but returning vehicles do aerobrake. They kind of have to. Aerocapturing at Mars might be a better question.

-There are several limits to Earths atmosphere, depending on the definition, but they are mostly arbritrary. The atmosphere slowly grows thinner as altitude increases, and depending on definition, it could be detected quite far, if only by escaping hydrogen.

-Escape Velocity: 11.186 km/s Orbital Velocity for LEO: ~8km/s

-Technically you are affected by every piece of matter in the Observable Universe's (possibly beyond, but probably not) gravity, but practically, in Interstellar space you orbit around the center of the galaxy if you are stable.

-The ISS is 249 miles/400 km up, and stays at the altitude, with thrusters present to maintain the orbit. Countries involved with the program likely make decisions together.

-Everybody has done stupid things, but I've never heard of any astronauts smuggling things, especially as extra weight is expensive. ... in space apparently has a few difficulties, but I wouldn't be surprised if they'd tried it.

-Treatment of crime in the station is also likely determined by a committee of the different nations involved, but nothing serious has ever happened, and I don't know what minor crimes could even happen up there.

-SpaceX Dragon launches cost $57 million for example. The Apollo Program cost $150 billion, inflation adjusted, by 1973

IF there is a difference in information between my and Nova's post, trust him over me. I did this quick and dirty.

[NovaSilisko]

The Apollo Program cost $150 billion, inflation adjusted, by 1973

The issue there is actually separating overall development costs from per-flight costs. You'd need to know the cost of the CSM, the Lunar Module, and the Saturn V, each time, as well as the support infrastructure that goes into each mission. Just dividing total program costs by number of flights isn't going to give a good estimate. However, in a program with as many flights as the shuttle, I think you can use that method to get a decent estimate.

[CalculusWarrior]

There is a mod made by a dedicated section of the community called Real Solar System, which essentially scales the Kerbin system up to real life sizes, relocates some of the bodies, etc. to create an approximation of our real-life solar system. I've never used it personally (Real Earth requires something like 9 km/s to achieve orbit, comparable to a light Eve lifter in stock), but if you're interested in recreating some of the challenges real space programs have to go through, that mod's an excellent look into them.

[harbingerdawn]

Walter Schirra on Apollo 9

*Apollo 7

[cantab]

In real life two sorts of aerobraking/aerocapture have been used. Spacecraft orbiting Mars typically enter an initial highly-elliptical orbit using their thrusters then aerobrake down over multiple passes. Landers come straight from an interplanetary trajectory to a landing, and the returning Apollo missions did similarly. What has not been done in real life is going from an interplanetary trajectory to a closed orbit.

"In principle, the exosphere covers distances where particles are still gravitationally bound to Earth, i.e. particles still have ballistic orbits that will take them back towards Earth. The upper boundary of the exosphere can be defined as the distance at which the influence of solar radiation pressure on atomic hydrogen exceeds that of Earth's gravitational pull. This happens at half the distance to the Moon." - Wikipedia

Personally I don't consider the exosphere "real" atmosphere because it's not comprised of gas atoms/molecules interacting with each other, and will consider Earth's atmosphere as extending up to the exobase which is at 500-1000 km.

A spacecraft in interstellar space will orbit the Milky Way, in other words the combined mass of all the stars, nebulae, and whatever that are closer to the galactic centre than the spacecraft is. The central black hole is only a small part of that mass, except for a spacecraft in the galactic core. Because the Milky Way is a disc the orbits of stars tend to wobble up and and down as well as circling the disc.

The ISS's altitude varies. It can be boosted by engines, and will decay by atmospheric drag. The orientation of the solar panels is important - by putting them "edge on" to the prograde vector the orbital decay can be reduced at the cost of less solar power. A compromise is "Night Glider" mode, turning the panels edge-on at night while tracking the Sun normally during the day.

In the days of the Space Shuttle the ISS was deliberately allowed to lower before a Shuttle mission to give the Shuttle an easier time, then boosted afterwards. Now the Shuttle is retired the ISS is typically kept somewhat higher to reduce the energy losses.

Astronauts have certainly sneaked things on board. There have probably been arguments but no known fights. There was a strike on Skylab when the crew felt they were overworked - since then astronauts have been given shorter working days. There's no-one known to have had ... in space, but a married couple did fly together - keeping their marriage a secret from NASA! - so speculation happens.

[Kerbart]

(...)but then again, people up there get bored so i imagine they do stupid things too, like trying to smuggle something, people getting into fights and arguments, breaking stuff?(...)

Given the costs involved in getting the ISS in orbit, it would be incredibly stupid to lose it over things like “the crew doing stupid stuff due to boredom.†There are a couple of things that reduce the chances of that:

• Crew selectionâ€â€it's not like you interview somebody today and send them up tomorrow. After a ten year (or longer) training program you know who's qualified to be enclosed in a small space with other people and who's not (although apparently they can act differently on the surface of this planet)
• Making the mental well-being of the crew a priorityâ€â€I learned on Startalk Radio from astronaut Chris Hadfield that yes,
  (the video is not a trick video) and it's part of the efforts to keep morale of the crew up
• They're professionals who do their job. For the same reason submarine crews don't go cannibal on each other after a couple of weeks under water

[AmpsterMan]

To explain why 100km is the "you are in space"

At 100km, the velocity required for a plane to generate enough lift is equal to orbital velocity at that altitude. Therefore, at 100km, you are "in orbit" because you stop hitting the ground not because your wings keep you aloft, but because the earth is curving away from you just as you fall.

[Hannu]

-Is aerobraking used IRL? i realize there are not many interstellar flights coming into earth, but for example when a ship comes from moon orbit, does it burn retrograde to orbit earth? or does it aerobrake in upper atmosphere? is it a reliable manouver, or is it a risky last resort?

Couple of Mars orbiters have used aerobraking to circularize their orbit after capture burn. They have made tens of very gentle passes through the upper atmosphere. Nothing like KSP style. These orbiters did not have special heat shields.

Several landers have used aerocapture. They have typically made high speed reentry from interplanetary trajectory. That needs massive heatshields and protective aerodynamic fairings. All things, manned and unmanned, have also returned from Moon without deceleration burn as far as I know.

-What is earth's atmosphere real limit? that marvelous 70km point that separates being on earth from being on space? Since there isn't really a hard point where atmosphere just stops, how far away can atmosphere be traced?

There is no "real" limit. Small amount of air molecules escape and they can be detected at very large distances by using sensitive detectors. Many planetary probes have such plasma investigation devices. Drag may be significant up to altitude of at least 1000 km, depending on mission.

- What are earth's real escape velocity, and orbital velocity at minimum altitude?

What do you mean with real? Standard definition gives about 11.2 km/s. Orbital velocity of lowest practical circular orbits are about 7.8 km/s

- Are ships in real space always under the influence of a celestial body, don't they ever just float there? i imagine it can't happen in the solar system, but in interstellar space i guess you are not really "orbiting" or "escaping" anything, right?

The gravity field of a galaxy and nearby stars are dominant in interstellar space. You can be bound to galaxy or escaping it. There are also larger structures in universe galaxy clusters, superclusters etc. There is no known place free from gravity in visible universe.

- What is ISS's altitude? do they change it often or is it stationary? who "runs" the ISS and makes decisions like changing it's orbit and stuff?

It is about 400 km. Drag and correction maneuvers change it. I do not know who decide it.

http://www.heavens-above.com/IssHeight.aspx

[hugix]

there are spacecrafts that returned to Earth from interplanetary space. NASA's Stardust and JAXA's hayabusa missions returned samples from a comet / asteroid.

These capsules also used the atmosphere to slow down and used a parachute for the last minutes.

Stardust returned with a velocity of almost 13Km/s and reached about 34g.

[NovaSilisko]

Can we quit using the terms Aerobrake and Aerocapture incorrectly? This has been a peeve of mine for a long time.

Aerobrake: the slow reduction of an orbit by gentle passes through the atmosphere

Aerocapture: the aggressive reduction of an escape trajectory to a closed orbit by encounter with the atmosphere, generally only possible with extra heat shielding to accomplish this

Reentry: Basically an aerocapture that doesn't result in a closed orbit - ie, you land afterward (or explode and die)

[Gaarst]

Answer above are quite complete, just adding some (mostly useless) details.

1) The Apollo missions did not circularise before reentring: they hit the atmosphere at ~11 km/s but did a controlled reentry: keeping the angle at 6.5° not to bounce off the atmosphere. On the other hand the Galileo probe hit Jupiter's atmosphere at 48 km/s reaching 230 G but survived the reentry itself and slowly fell down into its atmosphere, again without orbiting Jupiter first.

2) There is no defined limit to Earth's atmosphere: the exosphere extends to at least 10 000 km above the ground. But commonly, the limit between atmosphere and space is set to 100 km (if you go above, congrats, you're an astronaut) but that's just an arbitrary limit.

4) You're always influenced by a body, even when escaping. KSP's SOIs can be compared (but not the same IRL !) to real life's Hill spheres. A body's Hill sphere is first, not necessarily a sphere, but all the positions when the body exerts the strongest gravitational force on another body; e.g: the Sun's Hill sphere extends to about half the distance to the next star (Proxima Centauri), so ~2 ly in the direction of that star. Then, PCentauri will exerts a stronger pull on you than the Sun.

5) The ISS is in a ~350-400 km orbit with an inclination of ~52°. It does change a little, and tiny regular burns are required to keep it on its orbit due to the very thin atmosphere slowing it down.

6) Astronauts are selected and trained for their psychological abilities: it is required that they can withstand months-long missions, solitude, working under life threatening conditions or under heavy stress and the loss of orientation in microgravity. So they very rarely do stupid things, but, as said above, it sometimes happens.

7) As the ISS is the result of strong internal cooperations between several countries (modules + crew from different nations), I think that a specific agreement has set the rules aboard the station, so no specific country would have to judge the said crime. To be confirmed.

8) The total cost of the ISS is estimated to over US$100 billion. A single launch of an ATV is over $350M, the space shuttle $450M (up to $1.5 billion for some estimations), a Progess cargo ~$100M (not sure on that one)... Overall you're looking at several hundred million US$ for any large launch to orbit, though that tends to reduce recently, especially with SpaceX. The Apollo progam costed about $150 billion overall; and a single Saturn V launch costs ~$500M in 1969 dollars, so about $3 billion today.

Edited August 19, 2015 by Gaarst

[Shpaget]

To explain why 100km is the "you are in space"

At 100km, the velocity required for a plane to generate enough lift is equal to orbital velocity at that altitude. Therefore, at 100km, you are "in orbit" because you stop hitting the ground not because your wings keep you aloft, but because the earth is curving away from you just as you fall.

This is the second time this comes up on these forums and I have to react again.

This makes no sense. What plane, with what wings, carrying how much cargo?

Edited August 19, 2015 by Shpaget

[_Augustus_]

How are people bypassing the filter?

Anyway, there is solid evidence from Americans visiting Mir that the Russians did bring vodka with them. And for the record, that was Mir in the movie, albeit a horribly inaccurate one.

And ... in space doesn't really work and has never been done. As a matter of fact it probably won't even work on Mars, you need at least 0.7 gee's for some reason (learned that in biology).

Edited August 19, 2015 by _Augustus_

[Sharpy]

as per 4) in plain interplanetary, interstellar and even intergalactic space you're always influenced by gravity of the surrounding bodies. To truly escape gravitational bonds you'd have to travel very, very far - way outside the local supercluster of the galaxies and far from filaments connecting the superclusters. In this space, while the superclusters still exert gravitational influence on you, the space expansion is faster than gravitational acceleration the clusters could exert on you. Stopping there, you will never fall into any of the clusters because they drift apart, away from each other as space expands, and they do so faster - their gravitational influence diminishes faster - than the matter located there would accelerate towards them due to that gravitational influence.

Though the scale of distances necessary is really staggering. Just one order of magnitude more and you're leaning on the edges of the observable universe.

Edited August 19, 2015 by Sharpy

[Nibb31]

-Is aerobraking used IRL? i realize there are not many interstellar flights coming into earth, but for example when a ship comes from moon orbit, does it burn retrograde to orbit earth? or does it aerobrake in upper atmosphere? is it a reliable manouver, or is it a risky last resort?

Every spacecraft that returns to Earth uses aerobraking. Apollo, Soyuz, the Shuttle. Even nuclear warheads. It's used regularly by space probes to enter Mars orbit too. It's risky, but once you know enough about the atmosphere, it works.

-What is earth's atmosphere real limit? that marvelous 70km point that separates being on earth from being on space? Since there isn't really a hard point where atmosphere just stops, how far away can atmosphere be traced?

It's gradual, so there is no hard limit. Most organisations and legal jurisdictions consider that outer space empirically starts at 100km, but the effects of atmospheric drag can be felt at much higher altitudes. The ISS experiences drag and needs to be reboosted from time to time.

- What are earth's real escape velocity, and orbital velocity at minimum altitude?

Google is your friend.

- Are ships in real space always under the influence of a celestial body, don't they ever just float there? i imagine it can't happen in the solar system, but in interstellar space i guess you are not really "orbiting" or "escaping" anything, right?

You are always moving relative to something. You are always under the influence of some gravitational body, even it that force is extremely weak.

- What is ISS's altitude? do they change it often or is it stationary? who "runs" the ISS and makes decisions like changing it's orbit and stuff?

The orbital altitude varies, as does the attitude, depending on whatever the requirements. The ISS used to orbit lower so that the Shuttle could reach it, but nowadays it sticks around 300 to 400km. It also turns around when visiting vehicles are docking so that the approach and docking occurs at the nadir (facing downwards). Atmospheric drag pulls it down, so they reboost it, usually with the engines from a visiting vehicle. Sometimes they have to go up or down to avoid debris.

These manoeuvers are planned jointly between the participating countries. Each module has a Mission Control Center in its own country, but the main ISS Mission Control is in Houston, Texas.

- Have astronauts done stupid things? i remember watching Armaggedon, and the token russian guy at the ISS had a bottle of vodka stashed away, i thought "wow, alcohol must REALLY be banned on the ISS" but then again, people up there get bored so i imagine they do stupid things too, like trying to smuggle something, people getting into fights and arguments, breaking stuff? engaging in baby making or other sexual activities?

Yep, they have. Too long to mention here. There hasn't been any sexual activites that we know of (there simply isn't much intimacy on board a spacecraft), but stuff has been smuggled onboard for personal usage or to be resold. There was a scandal on one the Apollo missions about stamps that an astronaut brought to the Moon to be resold. There have also been fights and arguments, and astronauts grounded for it.

There are plenty of books on the subject if you're interested.

- If a crime is comitted in the ISS, whose jurisdiction is it? has that ever happened?

It's probably like being in international waters. I'm pretty sure you'd get nailed by the government that sent you up.

- What's the real cost of launching an oribital mission, like an ISS supply run? what about the cost of landing on the moon?

It depends on the mission, the payload, the destination orbit. SpaceX charges 60 million dollars to launch an 11-ton payload to LEO. That doesn't include the spacecraft or any payload. ISS supply runs are much more than that.

Wikipedia says: "The Space Review estimated in 2010 the cost of Apollo from 1959 to 1973 as $20.4 billion, or $109 billion in 2010 dollars, averaged over the six landings as $18 billion each"

[Mazon Del]

In a video I once saw concerning the various legalities of space travel (and some problems we currently or will shortly have because of it) they brought up that right now space law basically treats the property of a given government as its sovereign territory, and thus even though the ISS is "international", if a given country owns a particular module, the common law of their nation applies there. In all technicality, the ISS is considered a "border free" zone if only because nobody makes sure that your passport and other papers are good for you to move between modules....and now I just thought up a humorous Papers Please mod....

[cantab]

This is the second time this comes up on these forums and I have to react again.

This makes no sense. What plane, with what wings, carrying how much cargo?

And it's been answered before. It's a ballpark figure based on a generic aircraft, rounded off to an exact hundred for convenience. With some searching you might find some of the work from Karman himself on the matter.

[Shpaget]

rounded off to an exact hundred for convenience

Makes sense. As much as "height of an average human, rounded up to a nearest hundred km".

Without mass, aerodynamic lift and buoyancy this has no meaning. Using figures for "generic aircraft" also makes no sense, since generic aircraft are designed to fly at around 10km and at much lower altitudes.

All aircraft experience centripetal forces in level flight, and all orbiting crafts experience aerodynamic forces. Dismiss that fact in this scenario is just pointing to a number and saying "That is a pretty one, let's pick that.". Which IIRC is exactly what Karman did when he didn't fancy the number he got by math.

[peadar1987]

And ... in space doesn't really work and has never been done. As a matter of fact it probably won't even work on Mars, you need at least 0.7 gee's for some reason (learned that in biology).

That sounds made-up. I can't think of any reason why ... wouldn't work in complete weightlessness, and as a matter of fact, they have shot some adult film scenes in a plane flying a parabolic arc, simulating weightlessness.

[_Augustus_]

That sounds made-up. I can't think of any reason why ... wouldn't work in complete weightlessness, and as a matter of fact, they have shot some adult film scenes in a plane flying a parabolic arc, simulating weightlessness.

They haven't actually, the studios just claim that to make more money.

[Dkmdlb]

Makes sense. As much as "height of an average human, rounded up to a nearest hundred km".

That's an exaggeration. 100 km is like 5 orders of magnitude greater than the height of a human. Are you really saying that Karman's estimate is 5 orders of magnitude off?

[benzman]

Makes sense. As much as "height of an average human, rounded up to a nearest hundred km".

Without mass, aerodynamic lift and buoyancy this has no meaning. Using figures for "generic aircraft" also makes no sense, since generic aircraft are designed to fly at around 10km and at much lower altitudes.

All aircraft experience centripetal forces in level flight, and all orbiting crafts experience aerodynamic forces. Dismiss that fact in this scenario is just pointing to a number and saying "That is a pretty one, let's pick that.". Which IIRC is exactly what Karman did when he didn't fancy the number he got by math.

I found this https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line to be an informative read.

[Shpaget]

That's an exaggeration. 100 km is like 5 orders of magnitude greater than the height of a human. Are you really saying that Karman's estimate is 5 orders of magnitude off?

I'm saying that Karman pulled the number out of his derrière.

I found this https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line to be an informative read.

Wiki article does not reference any specific aircraft, nor gives any specific numbers regarding what I said was needed for the calculation.

Funny enough, there is even the [citation needed], which I swear I didn't put in there.