PLASMA WIND TUNNEL TESTS

Re-entry is one of the key challenges our technology needs to tackle. The conditions when our PHOENIX space capsule is re-entering our atmosphere at orbital speeds of ~7800 m/s are incredibly demanding. In this article we want to share some detailed insights into this process and how we develop and test our technology to withstand such extreme conditions in Plasma Wind Tunnel testing scenarios.?

IAD. Decrease the Speed. Protect from Heat.?

Within the first 10 minutes of re-entry, 99% of the velocity is dissipated by PHOENIX’ Inflatable Atmospheric Decelerator (short: IAD) developed by ATMOS.

The IAD serves three major functions:?

First: Decelerate the PHOENIX capsule early at a high altitude in order to lower heat loads.

Second: Protect the capsule and its payloads from the still intense heat at re-entry.

Third: Decelerate Phoenix further to urban speeds for gentle splash downs.

This is also the reason why we call the IAD a ballute, since it is a mixture of an inflatable balloon and a high velocity parachute. Just before PHOENIX enters Earth’s atmosphere, the ballute is initially inflated with the help of an on-board cold gas system. At around 120 km above the Earth’s surface, when re-entry begins, a bow shock and a subsequent plasma flow form in front of the capsule, leading to a high convective heat flux towards the surface of the spacecraft (yes, that is exactly what was impressively visible in SpaceX’ starship livestream: https://www.dhirubhai.net/feed/update/urn:li:activity:7174100274116993025)

Open air inlets lead hot plasma into the IAD system, while active fans compress the air further in order to keep a positive pressure difference between the inside and the outside of the ballute, guaranteeing shape stability at all stages of descent. For a concise overview of PHOENIX re-entry stages, see our latest technology video:?

7 Minutes of High Heat Loads

As the atmosphere becomes denser, temperatures start rising fast. Just after three minutes of re-entry, the highest heat loads occur in real flight, with temperatures of more than 1270K (~1000°C).?

Plasma wind tunnels simulate the behaviour of air flow in respect to thermochemical processes and reactions at a point along the trajectory of a return vehicle.

Therefore, plasma is produced and accelerated towards the test article to conduct temperature and pressure measurements. In repeated tests we aim to generate thermal data with the air intake in open and closed state to demonstrate the ability of our heatshield.

Our aim is to prove our thermal protection system is able to withstand 7 min of plasma wind tunnel scenarios at peak loads to validate its structural integrity during real flight conditions in space.?

IAD Test Article

For all tests, we used a full-scale model of our air inlet prototype (see photo below). Both, the rigid heatshield and the air inlet are made of a ceramic matrix composite (CMC). More about the material to be found on our partner’s website: https://www.keramikblech.com/en/material/).?

The flexible part of our IAD is made of an aluminosilicate ceramic fabric and a metallic gas barrier forming what we call a ceramic fabric composite (CFC) which is an in-house development.

Test Results and Conclusion?

Our test campaign generated a wide range of valuable thermal data and insights into material and structural integrity. The tests showed conclusively that hot air can be taken from the hot boundary layer behind the bow shock wave to inflate our IAD. The CMC heat shield as well as the CFC inflatable material have proven to withstand the extreme heat loads occurring during re-entry, which is a prerequisite of our technology to bring precious payloads safely back from space.?

The Plasma Wind Tunnel testing campaign has been carried out with the help of the Institute for Space Systems (IRS) in Stuttgart, Germany. We are very thankful for the professional help and guidance of Prof. Georg Herdrich , Dipl. Ing. Pagan, Hendrik Burghaus M.Sc., Clemens Kaiser M.Sc., and Johannes Oswald M.Sc..