Abort to the ground does not make much sense to me, because if your lunar lander breaks, you probably want to go to lunar orbit and leave the moon rather than take your chances on the surface waiting for a rescue lunar lander to come pick you up. A future lunar base probably will not be able to afford spare/fueled-up lunar landers, but every lunar mission will probably have a spacecraft waiting for them in lunar orbit.

Abort to the ground also wastes a lot of weight in terms of additional structure and landing legs. Eventhough abort to orbit might have twice the delta-V as some abort to ground scenarios, if you look at the structural weights associated with this, you will find that abort to orbit will weigh about the same as abort to ground.

Abort to orbit also gives you multiple more abort scenarios, than abort to ground.

Using storable propellants, I estimate 200 kg for the structure (including the engines, avionics, etc.), 50 kg for the inflatable/pressurized bubble, and 50 kg for a weak ECLS (keeps 4 people alive for a few hours in a disaster scenario) based on the small portable ECLS carried on an Astronauts back within the heavier Apollo-style lunar space suits. I assume another 500 kg for 4 Astronauts wearing the lighter 10 kg “flight suits”. The heavier lunar space suits can be carried outside of the “ejection pod”, and can be carried within a second pressurized section of the lunar descent vehicle, where the Astronauts would do their real living during the exploration phase. This gives me 800 kg for the vehicle and the 4 Astronauts, which means that it will be approximately 900 kg of storable propellants for fuel to be able to abort to lunar orbit in all scenarios.

This is a 1,200 kg “ejection pod” that can take 4 Astronauts (or 500 kg) back to the waiting spaceship in lunar orbit under most scenarios, and it can also serve as a cheap or emergency lunar ascent stage if the “real” lunar ascent stage does not work. If you are planning a lunar mission architecture with single-stage/reusable/refuelable landers and with pre-positioning of cargo or other lunar base materials, then this cheap/emergency lunar ascent stage will give you a lot of extra flexibility.

Anonymous

The other thing is that one of the goals of the lunar ejector seat was having additional electrical and control redundancy so if you have a catastrophic electrical or control failure that you can bail out (not just mechanical failures like engine problems). If the whole crew cabin is the escape capsule, getting real redundancy might be harder.

But avoiding having to get 4 people out of a tight area each with their own rocket engines is probably a good idea.

~Jon

LLO velocity is 1650 m/s, so if you’ve slowed to less than 750 m/s, you can still get back into orbit with 900 m/s of dV (gravity losses are very low, drag nonexistent)- or land with 250 m/s of margin. If the main system drops dead early in the descent, you abort to orbit, if it dies at anything between 700 and 850 m/s you have your choice, below 700 m/s you have to land, so 1 km/s is plenty. The abort guidance system would be awake and ready to take over at any time, and would make the surface/orbit choice at a clearly defined point.

The escape system would be an integral part of the crew module that gets swapped out for a cargo module, so only manned flights would suffer the payload hit. If the crew cabin is minimal enough to start with, it *is* the escape capsule and the only separation event is the entire crew bugging out. No traffic management problem with four escape systems having to keep out of each others’ way…

Acceleration is mild, the main engine is sized for the emergency landing case, with throttling. This is a very promising concept for those missions where there is enough infrastructure for a prompt rescue mission within the life support limits of the bugout vehicle.

That’s a great idea, although I would have to go with Anonymous and have an ejection couch rather than a seat.

However, would adding that to the lunar lander drive up the overall price of the lander, thereby making it too expensive?

I think that this is a great idea.

I think that the idea would be better if you only designed this ejection seat with the delta-V for abort to orbit, and not for the ejection scenario of abort to landing.

You should also not worry about having individual ejection seats for individual Astronauts, and instead have one “ejection couch” or pod (like ejection system on F-111 fighter jet) for all of the Astronauts who are ejecting. Any scenario where one Astronaut needs to eject will be a scenario where all Astronauts need to eject. You will be able to save a lot of weight on redundant structures, etc. if you do this.

Lastly you should use a fabric or inflatable or “Bigelow-type” pressurized structure for all of the Astronauts to get into that is attached to your “ejection” mechanism.

If you make my above recommended changes, then you have basically created an “ejection seat” that is really a cheap lunar ascent module. The only difference is that a “real” lunar ascent module will have a lot more structure, avionics, ECLS capability, etc, than your ejection pod, but it would also weigh a whole lot more.

This ejection pod would make economic sense in lunar architectures where you separate cargo and human landing vehicles, and where you decide to pre-position equipment and facilities. The economic logic is that you don’t waste a lot of weight, delta-V and cost on an over-designed lunar ascent vehicle, because the ejection pod can get you back to lunar orbit (for rendezvous with your capsule) at extreme low weight and cost. You don’t want to use your ejection pod as a true lunar ascent stage for “normal” travel back to lunar orbit, but it sure could come in handy if your lunar descent has a mishap or if your lunar base malfunctions or if your “normal” lunar ascent vehicle is broken or delayed.

I bet that if you did your calculations you would find that you could design design something that could return 4 Astronauts (without their Space suits) to lunar orbit and that weighs 500 kg to 1,000 kg including fuel. You could probably use a few of the smaller RCS thrusters designed for Apollo/Dragon/CEV as the propulsion system, and you could ignore using a complex 6-DOF guidance system by assuming that you will get close enough to your rendezvous target that the CEV, etc. could use their delta-V to do the docking/rescue maneuver.

What do you think?

Anonymous

That said, the reason I was even thinking about this was precisely because “beefing up your margins and redundancy” can only take you so far. Most importantly it pressures you to move away from architectures that would be more reusable (single-stage systems), and technologies that provide better performance (cryogenic propulsion systems) in order to get only a little bit of extra safety. It’s the same reason why launch escape systems are used on rockets these days–until you have a truly reusable vehicle that you can fly a lot *in the environment you intend to use it in*, your vehicle reliability is never going to be that good. Adding an escape system can greatly increase that, even if the escape system isn’t ultra-reliable itself.

Sure, some subset of bailouts are going to result in losing a crew member or two anyway. But is that really better than a 100% loss rate for failures without an escape system? I don’t think the trades would end up going that way.

One other thing. If you use nitrous as the oxidizer for your ejector seat (say using an engine like the one XCOR recently announced), it would be possible to use a decomposition device to generate a breathable atmosphere for many days using the residual nitrous. There are also proposed methods for doing the same with an NTO/Hydrazine system, but the danger of contamination or incomplete decomposition are a lot higher (but then again if the alternative is a 100% chance of asphyxiation…I’d take my chances).

~Jon

A lot of how well rescue systems work depend on how much infrastructure is in place. The reality is that even with good escape systems, a transportation failure on or above the moon is going to be fairly dicey for some time yet.

~Jon

I think, now we better put the margins/redudancy on the main vehicule than on individual rescue devices. If you have to use such a scheme, assuming you reach without injuries the lunar surface, chances are you will be stranded with little air waiting for inexistent lunar rescue.

In the (far?) future, if a full blown lunar base with quick rescue transport is available, your idea could be interesting. Using lunar ressources to make fuel on site will help, assuming a reusable/refilable lunar VTVL transporter (cosmos 1999 like

I always remember the story by Henry Spencer where during Apollo training, there was a computer failure scenario during ascent. The guys flew to the orbit manually looking at charts just fine, but they ended up in the wrong plane. :/

And would the CEV have an airlock in the normal case? Or perhaps one can vent the atmosphere in an emergency and get in through the docking hatch.