6

A quick follow-up to Re-entry Heat Shield Alternative

Instead of looking for an alternative to heat-shield, I'd like to draw from analogous naval tactics I heard about; Back in the 1950's to 1960's, or thereabouts, in heavy weather, ships stream (or used to stream) oil over the waters for ease of passage.

Would it be possible for a re-entry capsule to use something similar to reduce it's re-entry velocity to relatively manageable levels? Say, nylon/silk threads/sheet after them - sort of like deploying a drogue, or even the chute in thin atmosphere. Pack multiple chutes, and discard each in stages as a function of air-speed, and atmosphere density.

What is the maximum re-entry velocity (I know this will vary depending upon the mass & form of the capsule - but say we're talking about Soyuz TMA-M) that would allow heat generated by passage of air to be dissipated without special shielding?

Community
  • 1
Everyone
  • 13,629
  • 2
  • 33
  • 141
  • How would pouring oil on the water reduce either roll or yaw? In heavy weather, your ship is being bashed about by 10-20ft walls of water hitting it; a surface coating of oil on those 10-20ft walls of water is going to make zero difference. – David Richerby Dec 21 '14 at 11:12
  • @DavidRicherby: Old sailors I spoke with mentioned the tactic dating back to the 1950s/1960s or thereabouts. I should have mentioned it's second-hand knowledge ... – Everyone Dec 21 '14 at 11:15
  • 1
    It does have an effect: http://deepseanews.com/2010/06/pouring-oil-on-troubled-waters/ – Hobbes Dec 21 '14 at 11:57
  • 1
    The technique is much, much older. – Deer Hunter Dec 21 '14 at 15:49
  • TY Hobbes, Deer Hunter – Everyone Dec 21 '14 at 16:29
  • Related: http://space.stackexchange.com/questions/5205/have-liquid-cooling-systems-been-tested-for-reentry-surfaces – Stu Dec 22 '14 at 14:37
  • 2
    Use of high altitude parachutes to decrease the mass of the heat protection system. – mins Dec 23 '14 at 15:21
  • @mins: Your link deserves to be more than a comment :) Methinks it would get more up-votes posted as an answer – Everyone Dec 24 '14 at 04:18
  • Done! I hope other persons will be able to provide additional information on this proposal. – mins Dec 24 '14 at 11:31
  • Check "gossamer drag augmentation devices". Parachutes don't really work as such in extremely tenuous atmospheres since the ideal gas law breaks down and the pressure isn't sufficient for parachute deployment even with slow reefing. But a light, long fabric would slow down the vehicle to deorbit. Problem is, this is a low drag application and you'd still hit denser atmosphere with speeds that require all the rest of the vehicle descent and landing system. It's more of an alternative (re)entry part of EDL systems, if you don't require precise landing ellipse due to uncertainties involved. – TildalWave Dec 24 '14 at 12:05
  • @Noordung The word parachute/drogue was used a loose term for such a fabric to increase drag as you describe (+: My intent with the question is two-fold. First, determine the maximum re-entry velocity at which a space-craft may re-enter without an ablative, second - determine whether any non-ablative mechanisms were experimented/suggested may be employed to reduce velocity in ultra-thin atmosphere – Everyone Dec 24 '14 at 12:47

1 Answers1

4

1. About maximum reentry speed, unshielded.

Not an answer, just some additional elements...

From wikipedia:

"An approximate rule-of-thumb used by heat shield designers for estimating peak shock layer temperature is to assume the air temperature in kelvins to be equal to the entry speed in meters per second."

(for vehicle speed see figure below).

Then it depends on the spacecraft material exposed to heat. The material must maintain its mechanical properties, and the temperature inside must be acceptable.

For current deorbit schedule, the reentry interface occurs at 102.3 km altitude, at 7,591 m/s. How much time will be needed for the compounds to melt at 7,823 °C (or the inside temperature unacceptable)?

figures will change when the reentry interface speed will be decreased, and so the landing trajectory.

2. About alternative atmosphere reentry methods

Alexander Bolonkin wrote an article (another version here) in which he proposes to use high-altitude parachutes to supplement or replace the heat shields.

Warning: The author looks like controversial.

"The widespread production of high temperature fibers and whiskers allows us to design high temperature tolerant parachutes, which may be used by space apparatus of all types for braking in a rarefied planet atmosphere.

The parachute has open backside surface that rapidly emits the heat radiation to outer space thereby quickly decreasing the parachute temperature.

The proposed new method significantly decreases the maximum temperature and heat flow to main space apparatus. That decreases the heat protection mass and increases the useful load of the spacecraft."

In the same article, he shows the effect on the STS orbiter (with different parachute sizes):

enter image description here

I don't know if this has been researched further, or even confirmed as valid.

Community
  • 1
mins
  • 5,033
  • 2
  • 29
  • 58