Comparison of crewed EDL systems

Those who have followed the developments in crewed space flight might have noticed that there are quite some differences between the operational capsules. Where the Crew Dragon has four large main parachutes, the Soyuz capsule only has one. It is not weird for people to ask why this is the case. A breakdown of the different EDL systems can be found on our mission pages. But here is a quick summary:

	Orion	Starliner	Crew Dragon	Soyuz	Shenzhou	Gaganyaan
Launch mass [kg]	33446	13000	12055	7150	7790	8200
EOM mass [kg]	15458	10886	9525	2950	3240	5300
landing mass [kg]	9300	6350 *	9525	2950	3240	3735*
Nr of drogue parachutes	2	2	2	1	1	1
Nr of main parachutes	3	3	4	1 + back up	1 + back up	2
Landing system	Ocean landing	Airbag land landing	Ocean landing	Solid rocket motor land landing	Solid rocket motor land landing	Ocean landing
Crew volume [m³]	9	11	9.3	3.5 - Re-entry module 5 - Habitation module	6 - Re-entry module 8 - Habitation module	8

EOM - End of Mission

* Command module empty mass

Comparing the US capsules

We have already written a blog post showing the heritage between Orion and Apollo and recently we have published a blog post on the drogue parachutes of the Orion, Starliner and Crew Dragon. The three parachutes are all developed by Airborne systems and rely on previous heritage. Notably the Crew Dragon parachutes, and the Orion main parachutes are identical in size. The Starliner’s parachutes in our renders are a bit smaller than Orion’s, but other sources suggest that they are the same size. The smaller size would make sense given the lower empty mass of the command module, where the same size would make sense from a joint development point of view.

This heritage or joint development is where the quad cluster of Crew Dragon comes from. When building the capsule, SpaceX opted to put all hardware in one reusable capsule where both Orion and Starliner use an expendable service module. The additional mass makes for a heavier capsule upon landing. When you have already chosen the parachute, the only design option you have left is to add an entire new parachute to the cluster.

Comparing the US capsules and Soyuz

The same analysis can be done for the US and Russian capsule. The Soyuz capsule has about the same habitable volume as their US counterpart, but it only uses a single smaller parachute. This is because the Soyuz capsule has an expendable habitation module where the US counterparts bring the habitation module back to earth. Another interesting difference between the US and Russian capsule is the deployment altitude. Soyuz deploys the drogue and main significantly higher than the others. This is due to the method redundancy included in the capsules. The US capsules have a cluster of parachutes, thus if one fails the others can take over, an example of this is the Apollo 15 landing. When the Soyuz main parachute fails the smaller back up parachute must be deployed. The time required to determine a parachute failed and the time required to deploy the backup has to be considered. This time translates to altitude, and thus a higher initial deployment altitude is required.

Soyuz and Shenzhou

When comparing Soyuz to Shenzhou one sees quite some similar design features, such as the disposable habitation module, but one can also see that Shenzhou is bigger than Soyuz. This means the main parachute is larger. Besides the larger main parachute, both capsules use a similar with a main and a back up parachute.

Closing remarks

Normally there would be some kind of conclusion or statement on what is best or what is desirable or wrong. however, in engineering there generally is not a best, just the best fit for a problem. All these capsules have their own distinct advantages and disadvantages. Where carrying four parachutes might be heavier, an expendable module might be more expensive. Where an additional separation system increases the complexity, relying on heritage parachutes might result in a sub-optimal design solution.