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Gemini in one way or another was a somewhat unique spacecraft. One such unique feature was having a ejection seat. While reading trough the document Development and qualification of gemini escape system a specific question came to my mind.

In the document you can read the following

the Gemini ejection seat is qualified for flightcrew escape from the Gemini spacecraft from pad aborts to 45000 feet (13.7km)

These ejections seats where mainly meant to be used in case of a Titan booster failure. Some small mentions are made of using them in case of a parachute failure but what about using the ejection seats during the late stages of reentry?

I could find another source quote

The test simulated conditions of maximum dynamic pressure following an abort from the powered phase of Gemini flight, the vehicle being positioned heatshield forward as in reentry.

I'm curious whether the approximate 45,000 feet limit was applicable only during ascent or also during reentry. Additionally, considering the crew was wearing spacesuits, what might be the theoretical maximum altitude/mach number from which they could safely abort during reentry?

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    $\begingroup$ The technical history of Project Gemini tothemoon.ser.asu.edu/files/gemini/gemini_technical_summary.pdf states that the operational (not qual) limit of the seats was actually 15K feet and gives rationale (p. 208). This seems to be in reference to launch though. What is needed to really answer this question is the mission rules, and I haven't found that yet. $\endgroup$ Aug 10, 2023 at 13:16
  • $\begingroup$ I'll try to locate information related to the topic. Additionally, regarding ejection procedures similar to those described (from late reentry to touchdown) — did the STS missions with ejection seats also have such procedures? $\endgroup$ Aug 11, 2023 at 9:03
  • $\begingroup$ There is some info on the Shuttle seats here space.stackexchange.com/a/19407/6944 $\endgroup$ Aug 11, 2023 at 11:02

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After going trough multiple documents and sources related to the Gemini ejection system I found a few sources which quote or have a small reference to the situation mentioned in the question.

Gemini and the paraglider

In the initial Gemini concept the spacecraft would make a controlled landing using a paraglider. In the document PROJECT GEMINI TECHNOLOGY AND OPERATIONS 1968 We find the first small reference of the ejection system being used during a paraglider failure after reentry

The ejection seat was to provide the flight crew a means of escaping from the Gemini spacecraft in an emergency while the launch vehicle was still on the launch pad, during the initial phase of powered flight (to about 60,000 feet), or in case of paraglider failure after reentry

This image shows what a normal paraglider sequence would have looked like.

Gemini Paraglider Sequence

In an interview involving Maxime A. Faget (aerospace engineer behind Apollo and Gemini spacecraft), we can potentially uncover some of the early motivations of having ejection seats instead of a launch escape tower:

Faget: Gemini was going to make a landing using a gliding parachute in the original concept, and they wanted to put ejection seats in it. In the event that something went wrong with the gliding parachute, instead of having a back-up parachute, they'd just eject. So they had the thing designed with ejection seats in it from the beginning.

In the interview, Faget expressed his preference for a system with a launch escape tower, similar to Mercury and Apollo, over the use of ejection seats.

In this glide flight phase, the primary emergency procedure involved the use of an emergency parachute system. If this failed or wasn't viable, an ejection seat served as a secondary backup. The parachute system was rigorously tested, undergoing evaluations over 20 times.

North American began deployment flights of the full-scale test vehicle for the Paraglider Landing System Program. The contract called for 20 tests to demonstrate deployment of the full-scale wing from the rendezvous and recovery can, followed by glide and radio-controlled maneuvering; each test was to be terminated by release of the wing and recovery by the emergency parachute system

Conventional drogue and main parachute

The transition from a paraglider to a conventional drogue and main parachute system, complemented by a two-point suspension system, brought about a new mandate. Now, in the event of a parachute failure, the suspension system must be jettisoned before initiating ejection. in Gemini Guide: SEAT EJECTION SYSTEM we can read the following:

In the event ejection becomes necessary, after deployment of main landing system parachute and while descending in the two point suspension, it is mandatory that the main landing system parachute be jettisoned before ejecting from the spacecraft.

This meant that the main parachute first had to be cleared before the crew could use their ejection seats. Sounds pretty risky to me considering this could occur at any critical impact height during the final decent.

Testing and rating the ejection system

From various sources, it's evident that the ejection system was deemed sufficiently reliable to execute an emergency ejection from the spacecraft during descent. Numerous high-speed sled tests were conducted to validate the system's functionality and ensure structural integrity.

The purpose of sled tests in the ejection seat development program was to simulate various high-altitude abort situations. Sled test No. 3 was successfully run on August 9

Of course we need to take in consideration that various high-altitude abort situations does not directly quote to a situation mentioned in the question but it gives a us a lot of room to think how the system would have been used.

Even more testing was done using the high powered sled at China Lake

Dynamic qualification testing of the Gemini ejection seat began with sled test No. 6 at China Lake. This was a preliminary test to prove that hatches and hatch actuators would function properly under abort conditions; no ejection was attempted. The test was successful, and qualification testing proper began on July 1 with test No. 7. The test simulated conditions of maximum dynamic pressure following an abort from the powered phase of Gemini flight, the vehicle being positioned heatshield forward as in reentry. Both seats ejected and all systems functioned as designed.

Ejection seat on the sled

As for digging into this topic there was one quote which kind of struck me and kind of summarizes the entire characteristics of the Gemini ejection seats. In the interview with Faget he says the following

The best thing about Gemini was that they never had to make an escape. Chris Kraft will tell you the same thing. If you ask him what he thinks about the ejection seats, he'll say, "I'm glad we never used them."

The use of ejection seats as an alternative in the event of a parachute failure seems viable under certain conditions and so was actually tested.

As already stated in the question of Gemini being a somewhat unique space craft it really stoot out as a testament to the balance between risk management and technological innovation. The ejection seats were an solution to specific challenges faced by the Gemini program, particularly with the initial paraglider landing system. Yet, as reflected in the words of figures like Maxime A. Faget and Chris Kraft, there was an undercurrent of relief that the system was never put to the real test.

I could also not find any questions either asked in interviews with crew members or from any radio callouts during descend that this procedure was part of the mission. Perhaps more info can be found in the book 20th Century NASA History: Gemini Mission Rules and Gemini Press Kit - ISBN-10:1893472469

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  • $\begingroup$ Nice answer! It's annoying that the mission rules are not readily available. $\endgroup$ Aug 15, 2023 at 16:31

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