Why doesn't the BFR/Starship have a launch escape system?

Question

This question let me wonder whether SpaceX' Starship has a launch escape system. It really seems to have none. The obvious question is why not, it sounds pretty negligent to me not to have some kind of emergency security system. The Starship is so big, why can't it have launch escape thrusters like the Dragon spacecraft? I remind that the death of shuttle Challenger's crew could have been avoided if the shuttles had such emergency system, since the crew survived the initial explosion. If Starship isn't gonna have a launch escape system, I'd say they didn't learn their lesson from the Challenger disaster (but that's obvious anyway since the shuttles didn't get such system anymore until their retirement).

Answer 1

If Superheavy fails during launch (or even fails to launch in an unsafe way) the Starship itself might well be able to just light its engines and fly a suitable suborbital trajectory to a safe landing spot (assuming it wasn't hit by too much shrapnel). By the time Starship normally separates, it is much too high and fast for anything like a launch escape, so the only contingency left is that Starship itself catches fire, or similar, on the pad, or early in the flight, despite the fact that its engines haven't lit up yet. That might reasonably be considered a low enough risk to live with.

They could also fly each new Starship unmanned to orbit and back, as a proving flight if they choose to, which should shake out most manufacturing defects.

Answer 2

You are not the first to raise this question! It's worth reviewing Tim Dodd's accessible and detailed evaluation of escape systems: https://everydayastronaut.com/starship-abort/

He draws attention to a number of considerations:

• escape systems are not a panacea.

So in the grand scheme of things, to date, a mechanical abort system has only saved lives twice, may have prevented one tragedy and in one case caused a death. So out of the 320 orbital human flights to date, only three missions in total necessitated the use of an abort system, or less than 1% of crewed launches.

(And to paraphrase one commenter: if our concern is around the reliability and stability of rockets, it is ironic that our solution is "lots more rockets!". There are significant concerns about a) putting powerful, hair-trigger rockets and their fuel right next to the passengers, b) difficulty of testing, c) risks around carrying said rockets back through re-entry.)

• the Challenger Shuttle disaster fatalities were caused by a series of failures at many levels.

perhaps the biggest problem with the Challenger disaster wasn’t a hardware problem, but a problem with program management and pressure to get that flight off the ground. It was known that they would be launching outside of the predetermined operating envelope of the SRBs and it was recommended to not launch that day.

(Of course, it doesn't matter what the cause of the failure is if you need to escape! But the big lessons lay elsewhere.)

• trust is earned.

So that’s why I think it’s vital we see these things fly, fly often, and fly over and over. Only then will I think there’s a proven reliability record that would make it a safe enough option to not have an abort system.

A point that I think is rarely made, is that commercial airliners don't need escape systems because we can perform acceptance tests on them. Airliners are taken on test/commissioning flights before and during delivery to their customers, where their airworthiness is evaluated and certified.

You can't do this with disposable rockets: every flight is a maiden flight! And this doesn't exclude the Space Shuttle here, as the extensive refurbishment required after each flight would absolutely qualify for a test flight, if it were airliner, before passengers were allowed on board.

But with cheaply reusable and autonomous rockets, it's a completely different story. By specifically targeting low-maintenance and minimal refurbishment, SpaceX can do test flights and cargo flights until all the hardware and procedural issues are ironed out and the Starships can launch with an airline level of confidence. It is this capability that is unprecedented, and which is unsettling the established view of launch safety. Of course, they may fail in this goal, but that's why the whole grand saga has become so exciting lately!

Answer 3

Elon Musk has been mostly vague about launch escape on Starship, but he has indicated that he expects Starship to be reliable enough to not need it, other than a possible capability for the ship (second stage) to be able to pull away from the booster earlier than planned as a type of abort. The assumption apparently being that while the first stage might need escaping from, the second stage would not. Whether this rationale of making a space vehicle safe enough to not require launch escape in all phases of launch will be accepted by the regulatory agencies such as the FAA and DOT, and customers such as NASA and ESA, is unknown at this time. However even if Starship is ultimately not allowed to launch humans from Earth, it still has tremendous potential for many other tasks, including transporting or housing humans who are already in space, as well as revolutionizing the ability to launch large payloads at low cost and high frequency, which could transform space exploration over the next few decades.

One of Musk’s more detailed statements about launch escape was made in 2016 at the International Astronautical Congress conference (transcript timestamp 26:29):

the spacecraft itself is capable of aborting from the booster ... Launch abort on the spaceship itself is kind of pointless, if you’re on Mars you’re taking off or you’re not taking off. You know, parachutes don’t work too well and [you can’t have] some standard abort system, and just how do you abort 100 people it’s just not feasible, the key is to make the spaceship itself extremely safe and reliable, and have redundancy in the engines, high safety margins and have [it be] well tested. Much like a commercial airliner. Like they don’t give you parachutes...the spaceship could separate from the booster and fly away from the booster if there’s a problem at the booster level.

Musk recently reaffirmed this philosophy in an answer to a question about launch escape at the February 10, 2022 Starship update (timestamp 1:04:32) at Starbase, where he said:

Starship will not have an independent abort system. But I think something that would make sense is to have the thrust to weight of the ship be enough that it could take off from the booster even if the booster has a failure at the pad level, so you get the thrust to weight of the ship at sea level above one, then even if something goes wrong with the booster the ship can essentially fly away from the booster. And so that’s something that I think would be important for carrying people, and also for high value cargo to have the ship have thrust to weight greater than one even at sea level, that would be like the nine engine version, and then even if you lost one engine I think you should still be able to do an abort. So I think for crewed missions we would essentially maybe detank the ship to some degree so that would have kind of a launch abort capability with the ship even if you lost an engine. That would be my recommendation.

Musk gave no indication of how second stage engine pre-chill would be affected by this approach, whether for example pre-chill can be designed out of the system, or if second stage engine pre-chill would begin on the pad as soon as fuel starts being loaded (or prior to astronaut boarding), and continuing through the count and launch. Or would there simply be an acceptance that launch escape is not instantaneous but would take several seconds to initiate. These are details that presumably could be worked out.

However Musk’s overall philosophy of making Starship safe enough to not need launch abort capability during all phases of launch sounds strikingly similar to what was accepted in the original design of the Space Shuttle, as you alluded to, which had phases of launch, most notably the first two minutes, where any major anomalies during those phases would be inherently unsurvivable. As well as virtually no chance of survival (pre-Challenger) of an abort that resulted in a water landing. Another similarity with Starship is that Shuttle astronauts rode to orbit inside of what was essentially a rocket stage. NASA’s rationale at the time, similar to Musk’s, was that the Shuttle would be tested thoroughly and have multiple redundancies, eliminating the need for launch escape capability during all phases of launch. To the point that early Shuttle astronauts rode to orbit wearing only coveralls and oxygen helmets which provided no protection from depressurization. This half a century ago opinion about the Shuttle eventually changed once the vehicle came under increased scrutiny after the 1986 and 2003 accidents. Musk seems to be asserting that space technology has now advanced to the point that the original Shuttle philosophy of the 1970’s can be reinstituted. Whether the regulatory and space agencies will agree with this assessment is nearly impossible to predict at this time.

However Musk seems confident that it will be allowed, based on his well known public statements made over the past several years about building Starships capable of launching 100 people to Mars. As well as his announcement in 2018 of a project to send several artists around the Moon in Starship as early as 2023, as well as the (currently unscheduled) Polaris Mission III. And also including his vision of eventually sending 100,000 people to Mars during a roughly 30 day period every 26 months on 1,000 Starships, a number which doesn't seem to include the additional Starship fuel tanker and cargo launches that would be needed to support this. The viability of this futuristic vision of launching tens of thousands of people to colonize Mars is likely decades away and using technology yet to be developed, and thus is beyond the scope of the question or this answer. I am only attempting to answer whether a launch escape system will ever be needed on Starship for launching people from Earth.

What regulators would likely be influenced by is that currently the safest way to launch people to space is in a capsule, and this will not likely change in the foreseeable future. SpaceX would have to prove that Starship can be made as safe as a capsule before it would be allowed to launch people to orbit in it. During the Humans to Mars virtual conference on August 31, 2020 Musk said that he expects to do hundreds of uncrewed flights before launching people on Starship. Again the question is whether this will be enough to satisfy regulators. Falcon 9 has successfully landed 165 first stage boosters in a row without mishap. If hypothetically SpaceX decided to start selling seats to tourists who want to ride inside the Falcon 9 first stage, the first thing regulators would likely ask about is launch escape capability. If the answer is, “there is none but we’ve landed the first stage 165 times in a row without any problems”, that answer might not be considered adequate.

A capsule is small and sturdy and less susceptible to destructive aerodynamic forces than larger vehicles. Robust and sturdy heat shields that are less susceptible to damage are more feasible on a capsule. Capsules also provide a proven safe method of landing. Especially important is that a capsule has the ability to handle a much larger number of anomalies that might occur during all phases of launch and landing, including aborts that result in a water landing.

And while not a given, a capsule has a reasonable chance of surviving a first stage or even second stage booster explosion that occurs prior to launch escape activation. Two data points for this are the survival of the Challenger crew cabin after the breakup, and the apparent survival of the Cargo Dragon CRS-7 capsule after the second stage exploded. There is evidence that the CRS-7 capsule would have survived if it wasn't for the unfortunate, and in my opinion inexcusable failure of SpaceX to include a routine in the Cargo Dragon software to deploy the parachutes in a launch anomaly. This lack of foresight resulted in the loss of a large amount of expensive customer cargo for many countries and agencies, including an international docking adapter that was to be delivered to ISS.

Starship is a second stage which will have the capability to land propulsively. And this is where they propose to place the passengers, inside the second stage. Any failure of the second stage's propulsion or control capability during launch or landing that removes the ability of the stage to make a controlled propulsive landing would be unsurvivable. And any breakup or explosion of the second stage would be inherently unsurvivable. Capsules of course are not totally without risk, there is the possibility of a fuel tank explosion for example. However in space that would be true for all vehicles. Once in space it's a level playing field, where capsules have little to no safety advantage over other vehicles. But the risk of fatality caused by a capsule failure during launch and landing is less than it would be riding inside of a rocket stage that produces 1,500 tons of thrust.

Musk made a comparison to airliners not having parachutes, but the FAA may consider this an apples and oranges comparison with little in common. Considering that in the past ten years there have been only three people killed in U.S. airline incidents, out of about 80 million flights. Even if a 1 in 10,000 accident rate could be achieved in spaceflight, it would still be over 2,000 times more dangerous than flying in an airliner.

Adding an escape pod or something similar to Starship is unlikely because of the added weight, cost, and complexity. In theory a capsule with LES could be launched on top of Starship, but that in fact would confirm exactly what I am referring to. Any of these approaches would greatly reduce the number of people that Starship can launch to orbit.

But even if Starship does not receive approval to launch humans from Earth, it can still potentially carry out the dearMoon (sic) mission, send people to Mars, etc., by acting as a space ferry, with astronauts arriving in capsules at a space depot, or perhaps docking directly with an already fueled Starship. In fact this method is exactly what is planned for the Artemis III Moon landing, which NASA still maintains is planned to occur in 2025.

Musk’s belief that space travel should become as safe and reliable as airplane travel is certainly a goal that no one would disagree with. What is uncertain however is whether this goal is achievable, and if it is, whether the timeline to accomplish this will ultimately be measured in years, or in decades. And as applies to this question, whether Starship without launch escape capability could even come close to meeting this goal.