Why don't unmanned launch vehicles include launch escape system for payload?

Question

Mention of Launch Escape System (LES) brings to mind images of the crew on board a spacecraft ejecting at launch; the crew being the most valuable cargo on board.

Launch vehicles may also be unmanned, e.g. PSLV/GSLV, Ariane, etc. In this case, the most valuable cargo on board is probably the satellite(s) it carries to orbit.

• Was a case ever made to preserve the pay-load on board in the event of a failed launch by means analogous to LES?

• Why don't unmanned launch vehicles at present include LES for their pay-load?

Answer 1

Proposed Russian spacecraft, for Mars, Lunar, or orbital tug missions that would have used a nuclear reactor, did provide escape tower like functionality for the reactor.

But the issue is that the entire payload stack, is usually too big to save with an escape tower (and still have any payload left to go to orbit, due to weight of escape system). In the manned case, usually everything BUT the minimum to save the people is discarded. Similarly in the reactor case, it would save the reactor, but not the rest of the payload.

Another way of looking at, is Launch Escape systems are typically used, when Flight Termination Systems are not really good options.

If you terminate a flight with people on it, that really would suck.

If you terminate a flight with a nuclear reactor on it, as it flies over land, that would really suck as well.

In those case, it can be worth having an escape system, to avoid those consequences.

Answer 2

@Philipp has nailed it in his answer in my opinion, and we've, in a sense, discussed the economic viability of such payload escape systems versus insurance cost before in our main chat room, too. Technical and economic feasibility studies of such payload escape systems have however been done before, one such good example is Fred E. Wagner's thesis on EXPECTED VALUE ANALYSIS FOR AN UNMANNED EXPENDABLE LAUNCH VEHICLE PAYLOAD ESCAPE SYSTEM (PDF).

Truth of the matter is, that if the cost to launch the additional mass of such a payload escape system is at least near or even more than the insurance for your entire payload (might be many satellites, mind you), it's simply not worth it. And that's not even accounting for the cost to design, manufacture, and test such a system. So it was never really attempted.

NASA runs a Payload Safety Working Group (PSWG) via its Office of Safety and Mission Assurance, that is mostly involved with preparing procedures to assure safety of the payload and its handling crew during transport, payload integration, and so on, and publishes them in Expendable Launch Vehicle Payload Safety Program documentation (PDF). Here's a cool chart of the Safety Review Process (Source: NASA's Powerpoint presentation on Expendable Launch Vehicle Payload Safety Program, prepared by Cal Staubus):

   

But to my knowledge, no launch system offers to its customers a payload escape system that would be mounted to the payload fairing and land all of the payload safely in case of in-flight launch failure.

This of course doesn't exclude that some individual payloads might be designed for later retrieval at the end of the mission they were designed for, or could activate some custom launch escape and landing system in case of failed launch. I'm however not aware of any that would be designed for that, or if it is even technically feasible to jettison the payload out of the payload fairing during failed launch, even if you connect it to the range safety system and would receive jettison command prior to activation of the launcher's self-destruct mechanism. In such scenarios, there simply isn't any time to waste. You're trying to save human lives first, then worry about some fancy gadget that wanted to go to space.

Answer 3

Weight is a major factor... every item on the vehicle has to have a good reason to be there. Rather than trying to save an expensive payload in the event of a launch failure, it may be simpler/cheaper to maximize the reliability of the launch system, and accept the cost of losing the entire vehicle and payload in the (presumably rare) event of failure.

Even in the manned case, there is still the possibility of a failure for which no escape is viable. It becomes a calculated risk... minimizing but never really completely eliminating the possibility of losing crew/passengers to some mode of catastrophic failure.

Answer 4

Besides reasons mentioned by others - humans are more durable against "impact" type stress than usual orbital payloads are. The satellites are calculated to withstand the sustained several g of rocket acceleration, but not a single ~80g shock of hitting the ground. That means their emergency system would have to be far more advanced - provide much more gentle fall - than the one meant to save humans, or the satellites themselves would need to be engineered with impact shock durability in mind, adding to their weight and complexity in a way that is quite unlikely to ever be of any use.

Answer 5

It's simple economy.

Unmanned payloads can and usually are insured against loss due to launch complications.

The insurance costs less than the additional cost to install a launch escape system.

Answer 6

Another difference between human spaceflight and uncrewed launchers that isn't mentioned in the other answers:

Capsules for human spaceflight are used for both ascent and return, so are designed to land safely with people in them. That means they have parachutes, crushable structures to absorb the shock of hitting the ground or sea, and flotation devices to ensure that they don't sink while waiting the recovery.

The job of a launch escape system is to get the crew capsule away from a malfunctioning launcher, and high enough that the existing descent and landing system has time to function before the capsule hits the ground. The additional mass of the launch escape system is basically just the separation rocket.

For a satellite launch, because the payload isn't supposed to come back, it lacks all of these things. The added mass needed to include them would be considerably higher than just the separation system.