US crewed capsules
The US was the second nation to launch an astronaut into space. The first two flights onboard Mercury-Redstone were suborbital and later orbital flights were performed with the more powerful Atlas launcher. After JFK made his famous "we choose to go to the Moon" speech in 1963, the Apollo capsule was developed to enable astronauts to reach the moon. To help the Apollo research, the Gemini program started practising multi-crew flight, spacewalks, and docking. After the Apollo era, the Space Shuttle was developed. The latter performed a glide entry
, did not use parachutes for the descent,
and is thus not discussed here.
After the Space Shuttle era, the US initiated the commercial crew program. This program aimed to build an American launch system to launch American astronauts to the ISS. This would free up the research and development of NASA so they could focus on other missions. Several companies were selected for the initial development. Only two projects reached the end phase: the SpaceX CrewDragon and the Boeing Starliner.
The Artemis program, a follow-up of the Constellation program, was announced with the objective of bringing humans back to the moon and later to Mars. The capsule developed for this program is the Orion crew capsule.
Side by side render of the US crewed missions excluding New Shepherd
Mercury
Operator: NASA
Mission: Bring astronauts to LEO
First flight: 1961 (uncrewed)
Status: Retired (last flight 1963)
Mercury was the first US crewed capsule. The capsule was designed for a single person and flew both sub-orbital and orbital flights. The capsule flew on many different rockets such as Little Joe, Big Joe, Redstone and Atlas. The latter two carrying a crew. As the first two crewed flights were suborbital the re-entry velocity was much lower than in orbital flights. This reduced the requirements for the heat shield. The first two Mercury flights were thus flown with a passive heat shield. For a safe landing, Mercury had a single drogue and a single main parachute. To ensure crew safety in case of a parachute failure, a backup parachute was included.
The capsule would land in the water where it would wait for the US Navy to retrieve the crew. To dampen the impact of the landing, a skirt was included which was deployed just before landing.
Mercury in the water after landing
Gemini
Operator: NASA
Mission: Bring astronauts to LEO
First flight: 1964 (uncrewed)
Status: Retired (last flight 1966)
Gemini was the second crewed US spacecraft after the Mercury missions. The Gemini missions were flown to develop technologies required for the Apollo moon missions. The Gemini capsule made use of a conical ribbon drogue parachute that slowed down the capsule before main parachute deployment. The vehicle had a single main parachute that allowed for the mission to land on the water safely. The water landing was, however, not the first choice. The Gemini capsule was supposed to have a Rogallo wing for a horizontal land landing. Throughout the development of the Rogallo wing, many challenges were encountered, leading to the cancellation of the idea and adding a regular parachute to the capsule instead. A blog post on alternative Gemini landing systems was written and can be found here. The intention to use a Rogallo wing can be seen in the general design of Gemini where it re-orientated the capsule to a horizontal orientation just before landing. Another unique feature of Gemini (at least for US capsules) is the inclusion of an ejection seat over a launch escape tower used for Mercury and Apollo.
A variety of missions
After the success of the first Gemini flights, copious design concepts had been proposed as modifications to the existing capsules design, of which some were more realistic than others. There was for example a proposal for the Gemini capsule to serve as a rescue spacecraft in case the Apollo crew members would be stranded in space during a mission. [1] Several other proposals were made where the Gemini capsule would be used to carry astronauts to potential space stations such as the MORL for example, or proposals to launch a large version of the Gemini capsule, called Big Gemini, as a manned space station with 9 to 12 astronauts on board.
After the cancellation of the Dyna-Soar and the winged Gemini, the United States Air Force proposed a variation of Gemini, called Blue Gemini or Gemini-B. The capsule would act as a transfer vehicle between Earth and the proposed Manned Orbital Laboratory (MOL), which was supposed to act as a manned spy station. Eventually, only one unmanned test flight of Gemini-B occurred in 1966, followed by the program’s cancellation in 1969, primarily caused by the rapidly improving performance of unmanned spy satellites. [110]
Gemini just before landing.
Some more daring concepts were proposed, that aimed to launch Gemini further than low-Earth orbit. One proposal would use a Gemini spacecraft to explore the potential landing sites for the Apollo missions by performing a lunar fly-by. Another more challenging concept proposed to expand on the existing Gemini designs to use them as the return vehicle for the Apollo program. At some point, even the feasibility of a Gemini mission to Mars was investigated by General Electric, featuring a nuclear-powered space plane, similar in appearance to the Dyna-soar [110]. There have been plenty more Gemini mission proposals that never saw the day of light, however, for the scope of this blog post, only a selection was covered. Because most of these concepts were merely proposals, there is not much detailed information available on the recovery systems that these would have used. It is however very likely that much of the already existing Gemini recovery system would have been used, as most concepts only deviated mildly from the flown capsules.
Apollo
Operator: NASA
Mission: Bring astronauts to the moon
First flight: 1966 (uncrewed)
Status: Retired (last flight 1975)
The Apollo project led to the culmination of the space race between Russia and the US with the moon landing in 1969. The crewed lunar missions provided challenges by themselves for the Entry Descent and Landing system. The entry velocities of Apollo were in the ballpark of 10 km/s whereas the Gemini re-entry was in the order of 7 km/s. Apollo 10 carries the record for the fastest crewed re-entry with 11.09 km/s. The increase in velocity led to two significant issues. First, there is more velocity to bleed off before the capsule reaches the ground and second, the thermal loads on the heat shield are much higher. To mitigate this problem Apollo flew a controlled trajectory pitching up after atmospheric entry. This led to a horizontal atmospheric leg during the entry flight. Apollo did not pitch up high enough to leave the atmosphere and thus did not fly a skipping entry. After the entry, Apollo deployed a combination of drogue parachutes and main parachutes for a safe landing. The capsule was equipped with three main parachutes for redundancy. This was demonstrated in Apollo 15 where one of the main parachutes failed to inflate properly, but the astronauts still landed safely.
The Apollo capsule was the first US capsule to fly in three different programs or missions: Apollo (the US lunar program), Skylab (the first US space station), and the Apollo Soyuz Test program (the first US and soviet cooperation in space.
Crew Dragon
Operator: SpaceX
Mission: Bring astronauts to the ISS
First flight: 2019 (uncrewed), 2020 (crewed)
Status: Active
The SpaceX Dragon2 capsule or CrewDragon is the other crewed capsule that is part of the Commercial Crew Program. For SpaceX, this is not the first capsule to parachute back to earth. The first Dragon capsule was also part of the commercial resupply missions. SpaceX thus already had experience with bringing items to space and back.
Drop test of the Dragon 2 parachute system
Parachute system
The Dragon 2 parachute system is quite similar to the other crewed capsules as it has a drogue parachute and main parachute system. The drogue parachute is a cluster of two parachutes for redundancy reasons. The main parachute is a somewhat unconventional cluster of four main parachutes. Even though it is not the largest parachute cluster, that honour goes to the Kistler K-1 parachute cluster, it is still quite unique. It is unknown why SpaceX went for a four parachute cluster. One of the reasons to increase the number of parachutes of the clusters is if a parachute is already designed and build. However, SpaceX states that the parachute system for the Dragon2 has been completely redesigned from the Dragon capsule as the requirements are different. The only reason to increase the number of parachutes in the cluster then is to decrease the size of a single parachute. This would be mainly a production-related reason.
SpaceX had quite some issues with their parachute system. From interviews, it was understood that primarily the asymmetric loading of the parachutes was a significant problem. This can be an issue when one parachute in the cluster inflates earlier than the others, or when the parachute canopy inflates asymmetrically.
"Parachutes look easy, but they are definitely not easy." - Elon Musk
In June 2020 SpaceX flew its first crewed mission from American soil. The mission lasted about 100 days before the crew returned to earth, marking the first American crewed water landing since the Apollo Soyuz Test Program (ASTP).
The unique four parachute configuration of the crew dragon has led to some issues with a lead-lag in the cluster. Lead-lag condition means that one of the four parachutes takes longer to inflate than the other three. This was observed during the Crew 2 landing. Similar issues have been observed, but not released, for cargo missions.
Starliner
Operator: NASA, Boeing
Mission: Bring astronauts to the ISS
First flight: 2019 (uncrewed)
Status: In development
The Boeing Starliner is one of the two participants in the NASA Commercial Crew Program. The capsule, made by Boeing, will bring astronauts back to the ISS in 2021. The vehicle is set to launch on an Atlas V N22. So far the capsule has completed several parachute tests including a pad abort test. The capsule has made one orbital flight that was partially successful. A second uncrewed orbital test flight was performed for may 2022. Withi this successful flight a crewed test flight is expected at the end of 2022.
Landing system
The Boeing Starliner is the first US crewed capsule to land on land. The final kinetic energy needs to be absorbed to bring the capsule to a standstill. This is done using an airbag landing system. Earlier use of the airbag system includes the Mars landers Spirit and Opportunity.
Airbag systems are in general heavier compared to, for instance, the retrorocket landing system used on the Soyuz capsule. However, as the airbags can be inflated and stay inflated, they can be considered a passive system. In other words, no actuation is required at an exact time or altitude. This tends to make the system safer.
Drop test of the Starliner
Landing tests of the Starliner
Parachute system
When looking at the Starliner's parachute system, one can see that about ten parachutes are required for a successful landing. Two parachutes remove the back thermal protection cover. Two drogue parachutes are deployed. These ensure the capsule slows down to velocities where the main parachutes can operate. A combination of two parachutes is most likely used for redundancy. In case a single parachute fails, the system can still safely land the astronauts. After the drogue parachute flight phase, the main parachutes are deployed. These are deployed using pilot chutes. This is likely done as the main parachutes are too voluminous to fit in the mortar deployment system. The pilot chutes are also used to remove the main parachute from their parachute bags. These bags make sure the parachute system reaches line stretch before parachute inflation.
Testing
The Starliner parachute system has gone through extensive testing, which included system tests, drop tests, and a pad abort test.
Boeing has performed several drop tests from both helicopters and balloons. These various tests proved the sequence of events required to deploy the parachutes. Helicopter tests primarily showed the operations of the main parachutes as the drop was performed from 3.4 km. The balloon, which could fly up to about 11.5 km, allowed for testing the full parachute sequence including the drogue parachute.
During the pad abort test, Boeing demonstrated the full sequence of the parachute system. The objective of the test was to show that the launch abort system can safely extract astronauts in case the rocket fails. During the test, it could be seen that one of the main parachutes did not deploy. It was later determined that the parachute was incorrectly rigged and that the pilot chute was not attached to the main parachute due to a missing pin. This meant that, even though the pilot chute was ejected from the mortar tube, the main parachute was not pulled out. One of the philosophies of using a parachute cluster is to add redundancy, meaning that the capsule is still able to land safely under its two parachutes. Therefore, Boeing deemed the test a success.
Drop test of the Boeing Starliner showing the parachute sequence.
Orion
Operator: NASA
Mission: Bring astronauts to the moon
First flight: 2014 (uncrewed), 2022 (lunar uncrewed)
Status: In development
Orion is the latest capsule developed for NASA, produced by Lockheed Martin (capsule) and Airbus Defence and Space (service module). The system is capable of bringing 2 to 6 astronauts into orbit and beyond. Orion is intended to carry astronauts back to the moon in NASA's Artemis program. Future missions of Orion once included, the now-cancelled crewed asteroid redirect missions and possible crewed Mars missions. Originally Orion was to fly on top of an Ares 1 rocket, but this was cancelled in 2010.
Atmospheric Entry
As Orion is designed for a Moon mission, the entry velocities will be much higher than those for an ISS or LEO flight. The thermal protection system of Orion is thus designed for the higher heat loads. The material of the Orion TPS is similar to that of Apollo, but the production method has changed. Where Apollo glued a honeycomb to the structure and then filled that with epoxy. Orion makes TPS tiles which are then glued to the structure in a particular order. Early 2021 it was announced that Orion would perform a skipping entry to reduce the heat loads on the heat shield. If this is done during the Artemis 1 or Artemis 2 mission, it will mark the first skipping entry of a crew rate capsule.
Parachute system
The Orion decelerator system consists of a total of 11 parachutes. Three to pull the thermal back cover away from the capsule, two drogue parachutes, three pilot chutes, and three main parachutes. The various parachutes show the redundancy that is required for a crewed mission. When comparing to the Soyuz, one can see that the Orion capsule prefers a more redundant and thus heavier system. It is much more like the Boeing Starliner with a cluster of parachutes.
One can note that the Orion parachute system resembles the Apollo parachute system. Apollo also used two drogue parachutes, three pilot chutes, and three main parachutes. A more detailed comparison of the Orion and Apollo EDL systems can be found in our blog post.
Apollo (top) and Orion (bottom) heat shields.
The EFT-1 flight launched Orion onboard a Delta Heavy. One can see various phases, including aerothermal heating and parachute deployments.
Landing
The capsule will land in the water and will be retrieved there by the US Navy. This makes the system very comparable to the Apollo landing system. At some point, however, Orion was to touchdown on land. This was to be done using an inflatable landing system.
As the capsule lands in the ocean, no landing system is required. The only additional hardware includes floatation devices to force the capsule to float in the correct orientation. At some point during the development, Orion (then part of the Constellation program) was equipped with an airbag landing system to allow for land landings. The idea was that a land landing would allow for easier reusability for the Orion capsule.
This is very comparable to the Boeing Starliner capsule. It was considered not to have an airbag system on the outside of the capsule but on the inside. These airbags were placed into the astronaut seats. This resulted in an airbag system per person, leading to a lower overall landing system mass.
Testing
The first orbital test of the Orion capsule was flown on top of a Delta Heavy in 2014 as part of the EFT-1 flight. The capsule spend about 2.5 hours in space reaching 5800 km and re-entered at 8.9 km/s demonstrating the thermal protection system of the capsule. The next orbital flight is expected on top of SLS as part of the Artemis 1 mission launched in November 2022. Orion will perform an uncrewed flyby of the moon. On December 11th Orion returned to the earth's atmosphere and quickly jumped back out. This skipping entry marked the first time a crewed capsule performed such a feat. After the second entry, the 11 parachutes deployed as they were expected to and Orion splashed down after a good test flight.
The first crewed flight of Orion is expected as part of Artemis 2 in 2024.
New Shepard
Operator: Blue Origin
Mission: Suborbital flights
First flight: 2015 (uncrewed), 2021 (crewed,)
Status: Active
New Shepard is a reusable US commercial crew vehicle designed by Blue Origin. It is designed to perform suborbital flights carrying research payloads and private astronauts. The booster separates from the capsule 2mins 45sec into the flight after which the capsule passes through the Karman line spending a short period in space before beginning its re-entry. Due to the vehicle’s suborbital trajectory and low apogee, minimal heat shielding is required. At an altitude of roughly 2000m [22], the capsules three drogue parachutes deploy followed shortly by a cluster of 3 main parachutes. Finally, the vehicle fires a retro rocket shortly before touchdown to ensure a soft landing in the West Texas desert. Blue Origin has prioritised safety with this vehicle, ensuring that every system is redundant this includes the parachute system which it claims is capable of safely landing the capsule even if just one of three main parachutes deploys. In this case the vehicles retro rocket that fires just before touch down in order to ensure a safe landing is able to be adjusted to give a higher maximum thrust to compensate for the higher decent rate [23].
Flight path of New Shepard
