Deployable thermal protection systems

Since the days of Viking inflatable or deployable thermal protection systems have been a holy grail of EDL systems. Their ability to combine the function of a drogue parachute and heat shield allows for a significant weight reduction of the overall lander. Especially for Mars missions, this is a very sought after solution. This page gives an overview of missions flown in support of deployable or inflatable thermal protection systems

In September 2022 ISRO launched an inflatable aerodynamic decelerator on top of a sounding rocket. The mission launched to about 80km where it was deployed from the nose cone of the rocket. The test mission was about 77 kg and the IAD measured 1.3 meters in diameter. The mission used compressed nitrogen for inflation at 110 seconds after lift-off, enough to pressurize the IAD to 1.1 bars. 

Not much is known about the mission but ISRO announced the mission to be a success. [147, 148]

In March 2022 the JPSS-2 will launch to space on board an Atlas V. Besides the earth observation satellite, a second payload called LOFTID will be launched. The Low-Earth Orbit Flight Test of an Inflatable Decelerator is an inflatable heat shield mission to demonstrate the full entry of this new technology. LOFTID is a 6-meter dish that will deploy using nitrogen after the centaur stage performs the de-orbit burn. The structure consists of an outer layer that can survive temperatures up to 1600 deg celsius and an inflatable structure that provides stiffness. After the re-entry phase is complete the data recorders are ejected and recovered separately. The HIAD itself will be recovered by a parachute system provided by ULA. 

ADEPT is a NASA program that aims to increase the technological readiness level of semi-rigid deployable aerodynamic decelerators that can be used to achieve a lower ballistic coefficient for interplanetary probes or Earth entry capsules. The program has undergone several phases of testing including material sample tests, arc-jet tunnel testing of scale models to recreate the thermal conditions of reentry, and wind tunnel testing to characterise the aerodynamic loads. [155][156]

As part of NASA's exploration of Mars, NASA would also like to explore the heights. To do this, NASA started the development of an inflatable aerodynamic accelerator [90]. Instead of deploying a parachute behind the vehicle, this is a system that inflates a "shield" in front of the vehicle. This can be combined with a heatshield material to be deployed before entry.

The IRVE missions served to develop this hypersonic inflatable aerodynamic decelerator (HIAD). In total, four missions were flown, which furthered the technological readiness of this system. IRVE's HIAD consisted of stacked toroid-shaped tubes with a half-angle of 60-deg, on which the flexible heatshield skin was attached on the outside of the HIAD.

The vehicle on which IRVE-I was launched on a Terrier/Orion sub-orbital launcher, limiting the vehicle's total mass to 100kg [93]. The stowed diameter of the HIAD fitted within the 30cm diameter vehicle. Once deployed, the HIAD diameter was 3m[91,92,93]. On IRVE-II, launched on a Black Brand, a phenomenon was seen which was not expected. This phenomenon was that during the dynamic pressure pulse, the HIAD would flex. Although some flexing was expected, it was not expected to flex to this degree [93,94].

To investigate the flexing and test the control system of the HIAD two new missions were flown IRVE-III & IV. These flew on the more powerful Black brant IX, which allowed an increase of the vehicle mass to 280kg and increased the vehicle diameter to 47cm [91,92]. The control system consisted of both a standard RCS system and a system to offset the centre of gravity. 

The ESA IRDT or Inflatable Re-entry and Descent Technology mission was four times a two-stage inflatable heat shield. The first launch was in February 2000 on top of the first Soyuz Fregat launcher. This qualification flight offers a great and cheap opportunity. The launch went perfectly, however, IRDT suffered a failure in the second stage. When all goes well IRDT deploys in two stages. During the first stage, it goes from 80 cm to 2.3 m and then to 3.8m in the second stage. This can be seen in the figure on the right. During the first flight, this second stage did not inflate properly. The vehicle hit the ground harder than expected and was retrieved several days later. The wreckage of the capsule can be seen below. 

After this "IRDT-Fregat" test flight there were to be three more flights. These were all launched on top of a Volna [Wave] rocket launched from a Delta III submarine. 

Overview of deployable TPS experiments