V0.2 - 17-04-2020
There are many developments going on in the world of Entry descent and Landing. These are not only in making parachutes lighter and stronger but also in new innovative systems such as deployable and inflatable heat shields. These systems, such as ADAPT and LOFTID, can combine the functionality of the drogue parachute and the thermal protection system enabling larger payloads.
Missions to Mars are getting heavier and more ambitious. All of the previous landings have occurred at low-level terrain, thus with the highest air density. Future missions are targeting higher altitudes. This means that parachutes are less efficient and have to become bigger and bigger. To take some load off the parachute systems engineers would prefer to make the capsule larger, increasing the frontal area, decreasing the Ballistic Coefficient, and decreasing the terminal velocity. However, the diameter of these missions is limited by the fairing diameter of the launcher. Solutions for this problem can be found in inflatable and deployable structures. These structures are stowed for launch and only deploy when required. At the moment there is quite some research being done into these systems. None have flown as part of an operational mission.
An alternative to the inflatable structure is supersonic retro propulsion. This concept is much like the Falcon 9 re-entry burn performed on earth. The vehicle will provide a delta-v with rocket motors embedded in the heat shield. This has two significant challenges, the first is that there has to be gas in the heat shield and the second is the complex interaction of rocket exhaust gasses with the supersonic freestream.
Artist impression of an inflatable heat shield in the Martian atmosphere