Deadly Reentry Mod

[Henri von Braun]

Hello everyone,

I have recently downloaded the Deadly Reentry mod, and I would like to permit my ship to reenter without blowing up. I have used the heat shields provided, bu they keep passing the 10 000 degree benchmark. I have checked out that real spacecraft have a specific angle to reenter. I would like to know what angle do I need to reenter , and if possible, how to measure them.

Thank you very much !

Henri von Braun

[chaosplacer]

You want a re-entry angle as shallow as possible. In reality, if you go too shallow, you kind of bounce of the atmosphere, that's why you need a specific angle that lies between bouncing and burning.

For KSP at the moment, just go as shallow as possible. Set your periapsis slightly below 60 km and you should be fine.

[Sovek]

Try a Pe of about 26 km. I've found that this gives a g force very close to what the original apollo missions experienced during re-entry. This in turn, should allow you you to re-enter with the heat shield.

[Wavelength]

Hey Henri, I too have been running the Deadly Reentry mod and in my experience have found between 25km and 30km to be shallow enough to, A: not burn up and B: not go back out into orbit. I rarely see temps over 4k. Another problem i have is the inflatable heat shield flipping me over when the drag gets high enough. By reentering between the 25 - 30 km range, ive found that yes, i do still flip over, but only after i have slowed down enough not to torch my kerbals. At that point i cut the thing loose and get the chutes out.

[Specialist290]

The "skipping back into space" concern exists in real life because most capsules only have a limited amount of time that their life support systems will keep the crew alive. The capsule itself would eventually return to Earth; it's just that, by the time it did, the crew would likely have been smothered by its own carbon dioxide (or starved, or dehydrated, or... well, let's just say it's not a pretty picture). In KSP that's not as much of a concern, unless you're playing with other mods like Ioncross Crew Support.

[Henri von Braun]

Hello,

Thank you everyone for your answers ! After quite a few tries, Bob finally made it through!

Thanks again for the help,

Henri von Braun

[Dunbaratu]

The "skipping back into space" concern exists in real life because most capsules only have a limited amount of time that their life support systems will keep the crew alive. The capsule itself would eventually return to Earth

So wait, when this effect is described as "skipping back into space" by the popular press, they're lying then? Because if all that's really happening is "the air slowed it down some, but not enough to completely kill the orbit" in no way is that even close to the act of "skipping" a stone on water. When skipping a stone, the stone would not have bounced up entirely on its own without the water being present. It still would have fallen and hit the ground of the water was missing. Therefore the water's presence is in fact *causing* the stone to bounce upward, imparting a force upward on the stone (and not just drag in the retrograde direction, but in fact a force that is actually upward). This is a terrible, terrible analogy if what's actually happening in shallow re-entries is that the air exerted no upward force whatsoever on the craft and instead exerted entirely retrograde force only on the craft (drag), and the air is not the slightest bit responsible for making the craft go back up into orbit at all, but rather the craft would have done that anyway and the air just failed to prevent it.

Water *causes* a skipping stone to bounce upward. That's not the same thing as air failing to STOP a craft from the going upward it normally would have done anyway on its own.

Is this another case where, when science is dumbed down for public consumption, it becomes incorrect?

[AngelLestat]

much science much science but nobody thought that a deadly reentry will never happen in kerbin?

The speed to leave kerbin´s orbit is 2000 m/s, in earth is 8000 m/s.

[Nibb31]

In most cases, if the re-entry is too shallow, you would shoot through the upper atmosphere without losing enough velocity to totally deorbit. However, it would lower your Ap and you would definitely deorbit several orbits later.

However, in real-life, capsules have a positive lift/drag ratio, depending on their angle of attack, therefore they can hypothetically raise their altitude if they are oriented in a specific way. This would be like a skipping stone effect. Again, you won't just bounce off into escape velocity. Any lift would be gained at the expense of velocity and the effect would be pretty much the same. You would reenter a few orbits later.

In the case of Apollo, once the Service Module was separated, the capsule wasn't designed to maintain power and life support for more than a few hours, so if something like this did happen, the CM would land in a random location with 3 dead astronauts (and probably no parachutes, which would be messy).

[Spectre211286]

if you have fuel left use your engines to slow you down i always click the retrograde button in mechjeb and take that angle and then slow down as much as possible. if no fuel left use an aerobraking maneuver and as many orbits as required to slow down enough to survive. i have used a fusion engine mod that gave me enough fuel to slow down sufficiently that i survived reentry without a heatshield.

[Sleipnir]

So what is the best approach angle then? I have tried setting my periapsis at 60km and it worked fine for my test probe, but once i tried it with a 1 man pod it didn't work and Bob died . So the 60km thing is not the final solution. I am guessing the mass difference had an effect on it. Can anyone help?

[Frederf]

I used to use a reentry mod that had an expendable ablative shield that would deteriorate depending on heat and time. If you were too hot for too long it would deplete the material and it would fail. If you entered too steeply the peak temperature or peak G would be too high and it would fail. The goal became to use the shield material up to spread out the energy of the interface over a long time without using it all.

Deadly Reentry seems a lot more simplistic. As far as I can tell it just has a temperature and no durability so the goal is to keep the stress on the shield low and make the duration as long as possible. With D.E. you want shallow angles (~5 degrees) at the atmo interface with minimal orbital energy (100x40km for example). There's no such thing as too shallow here.

Apollo also had lift created by the shape of the capsule so the attitude of the craft affected its path. The lift kept the craft from plunging too rapidly into thicker layers below and maintaining a desired deceleration for longer.

[Awaras]

To all those that have issues with burning up on reentry even when setting the PE to 60km - If you have the ferram aerospace mod installed, it seems to make reentries much less survivable.

[RoboRay]

DR is somewhat unrealistic in that the shallower your entry angle, the more survivable it will be. In reality, being too shallow is what leads to burning up (because you're exposed to the high temps for a longer period of time) while being too steep leads to structural failures from gee-loading.

If you are burning up with a Kerbin Pe of 60km, you have other mods installed that are messing up DR.

[Frederf]

Yeah I have Ferram but if it's DR or Ferram, FAR stays. I can still reenter safely just with a smaller margin. I also think FAR makes mechjeb not be able to calculate ship drag.

[N_Molson]

So wait, when this effect is described as "skipping back into space" by the popular press, they're lying then?

When returning from the Moon, no. The Earth "slingshot" effect can send the spacecraft on an escape trajectory. Or in an orbit so elliptic it will take months for it to come back. Also don't forget that KSP physics model don't take gravity perturbations into account. Sun/Moon/Earth interactions can send the spacecraft in an elliptic orbit around Earth that never crosses atmosphere again.

terrible analogy if what's actually happening in shallow re-entries is that the air exerted no upward force whatsoever on the craft and instead exerted entirely retrograde force only on the craft (drag)

You forget something that isn't (AFAIK) implemented in KSP : conical (Apollo) or headlight-shaped (Soyuz) capsules produce lift, like any shuttles or aircrafts. They are designed to produce lift when re-entering, and while they are designed to fly at their best at very high ultra-sonic speeds, they completely stall only slightly above Mach 1 (at trans-sonic speeds). When the capsule is tilted in the right direction (thanks to RCS thrusters), it acts as a wing : air pressure is higher on the heatshield, and lower above the top.

From Wikipedia :

In practice, capsules do create a significant and useful amount of lift. This lift is used to control the trajectory of the capsule. This controls allows for reduced g-forces for the crew, as well as reducing the peak heat transfer into the capsule. The longer the vehicle spends at high altitude, the thinner the air is and the less heat is conducted. For example the Apollo capsule had a lift to drag ratio of about 0.35. In the absence of any lift the Apollo capsule would be subjected to about 20g deceleration (8g for low-earth-orbiting spacecraft), but with lift the trajectory can be kept to around 4g.

So, when the capsule "skips" the atmosphere, lift is produced, and not only drag. Of course nothing can produce more lift than drag (else we wouldn't need engines !), but the effect is significant enough to greatly bend the trajectory of the spacecraft. This, combined with the slingshot effect, can be a one-way ticket when re-entering from lunar velocities (roughly 10,500 m/s vs "only" 7,500 m/s for a LEO return). And to escape Earth SOI, you don't need to go much faster than 11,000 m/s.

A spherical capsule (like Vostok) produces no lift at all, and only drag, typically getting 8-9g on re-entry. There is also a safety mode on the Soyuz that, if the other controls fail, make the capsule automatically spin on itself at a fast rate, which nullifies lift. This is called a "ballistic reentry", and the spacecraft decelerates exactly like a spherical capsule in that case. Soyuz TMA-11 re-entered that way, and was nearly 500 kilometers off-target, because of the lack of lift.

Edited November 15, 2013 by N_Molson

[Taki117]

Also with Deadly re-entry you have to take re-entry speed into account. If you are hitting atmo at over 2.5km/s you are going to get much hotter much faster. Best I've found is to have an apoapsis about 40km up and pray for the best. (It's usually keep the pod intact, but kiss your solar panel goodbye)

[Specialist290]

Knowing how old this thread is, I can guarantee that it's highly likely that none of the information is relevant to Deadly Reentry in its current release. If you want to continue the discussion on atmospheric skipping in the real world, then I'd highly recommend starting a new thread over in the Science Lab.

Thread closed. Have a nice day, everyone, and don't forget to check the posting dates