Utilizing existing
assets to create contingency ISS crew capability.
An excellent post by Henry Vanderbilt at the Space Access
Society,
and a lively discussion at Rand’s Transterrestrial Musings,
has prompted me to write up something I’ve been toying
around with for a long time; could the U.S. achieve manned access to ISS in a
short timeframe, if it was required to avoid abandoning ISS if we lost access
(for either political or technical reasons) to seats on Soyuz. This post
assumes that ISS, a 150 billion investment, is considered worth taking a few
risks to save.
First, let’s look at what we (the USA) actually get from
Soyuz access. We get, for each Soyuz, a maximum of two seats up and down,
because Soyuz must carry at least one Russian crewmember. Therefore, to replace
what we get from Soyuz, Dragon needs to carry only two.
For the sake of this post, I’m going to assume that Dragon
2, CST-100, and Orion, cannot be made flight ready in time enough to matter.
That leaves us with Cargo Dragon, a tried and proven unmanned spacecraft.
(Another ISS cargo transport, Cygnus, cannot be used because it lacks reentry
capability).
So, what would it take to enable Cargo dragon to carry two
astronauts? In a truly bare-bones, no-holds-barred concept, you’d place two
padded mats and two astronauts with
scuba rebreather rigs in the Dragon while horizontal, then launch as normal.
This is survivable, so it’s a baseline to show how close we are (or already
there) to true emergency capability. With a few small changes, it can be made
far better (safety equivalent to Shuttle) and that, IMHO, is more than good
enough for a contingency plan.
I looked into this in detail over a year ago, and I'll start
with the obvious first objection; no LAS (Launch Abort System) on cargo Dragon.
However, this isn’t exactly true, as there are survivable abort options for
much of the assent profile. Cargo Dragon has Draco (not super dracos as used on
the Dragon 2 LAS) thrusters. It thus has the ability to pull away from a
non-thrusting stack once past stage separation (due to miniscule aerodynamic
loading due to low air density). For an earlier LV loss, as we see on CRX-7,
the capsule has a good chance of surviving; had the parachutes on CRX-7 been
able to deploy, Dragon would have survived. So, in brief, with a few software
changes, Cargo Dragon is far safer from an abort-during-ascent POV than Shuttle
was (There were segments of the shuttle ascent profile where multiple engine-outs resulted in a "black zone" trajectory - non survivable for vehicle or crew. Further, pre Challenger, any ditching would have been non survivable, while post challenger it was merely probably unsurvivable, due to the egress pole system). In a case of emergency need, Cargo Dragon's existing capabilities (leveraged with a few software tweaks) are more than good enough IMHO.
Next, control systems; IMHO, a manned spacecraft needs a
manual override capability. This would require some software changes to Dragon,
plus the inclusion of a laptop computer (plus another for backup), joystick, and Ethernet cable (I think,
but am not sure, that the connection port inside Dragon is Ethernet type). This
is obviously bare bones, but for an emergency need, that’s good enough. The laptop could also serve as a data screen for the crew.
Life support; Cargo Dragon has a life support system, sort
of; it's enough to support mice, at least, as we saw on CRS-4. However, to support two astronauts, let's
assume it can (as it obviously does) maintain pressure and temperature, but
nothing else. What's needed is therefor O2, and O2 can be carried in tanks (commercially
available standard O2 tanks would be fine) simply secured inside the Dragon.
Either the crew breaths through masks, or a CO2 scrubber in the form of a
computer CPU fan plus a lithium hydroxide scrubber canister from a scuba rig
would, with active monitoring by the crew, do just fine. Obviously, this system
could be improved upon, and probably would be (just one example; computer
monitoring of O2 levels coupled with computer control of an O2 release valve)
but we’re talking bare bones capability here, where good enough is good enough.
Communications; Dragon already has a comms system, but no voice comms. The existing data path can be utilized for voice comms via a headset attached to a laptop, or directly to a port in the Dragon. This would require some software changes, but not hardware changes.
Docking; Cargo Dragon cannot dock, it berths to the CBM, and
thus requires crew inside the station for both arrival and departure. This is a
problem, sort of. The answer is, for arrival, the crew on ISS handles it like
it does now for arriving cargo dragons. Emergency evac is a different issue,
and absent some changes would require one crew-member to stay behind and
unberth Dragon, then do an EVA to egress the station and enter Dragon.
Thermal regulation; two astronauts should be within the
Dragon’s thermal regulation abilities, as evidenced by Dragon already having
flown several refrigeration units (which dump significant heat). The human body
at rest puts out about the same heat as a 100 watt bulb, so for two, or for a
short term, 4, astronauts, this should be manageable with the existing thermal
control systems.
Crew ingress to Dragon on the pad; this is problematic,
because the current pad and TEL have no crew access features. However, all that
is really needed is a way to get crew in, plus a couple of techs to button up
the hatch. This could be achieved via welding a small platform to the top of
the TEL, and using yacht-type bosun seats and pulleys to hoist the crew up
(that’s how yachtsmen get up their masts at sea, a feat which is sometimes
needful). Or, rent a crane and use a basket. As for emergency egress, ziplines
from the TEL would be easy (terminating next to an armored personnel carrier). If
the astronauts wore the zipline harness for launch, it’d actually be a faster
egress than the shuttle’s basket style zipline. (which also utilized an APC at
the bottom end).
Seating; Dragon would need seats in order to carry crew. It
would need two seats, though four would be preferable (in case of emergency
station evac needs). Life support that’s good enough to get two people to the
station could handle four for the far briefer time needed to get from the
station to Earth. Cargo Dragon has the needed deck mount holes for seating, but
it would need the seats themselves. It could either use some of the ones we saw
in the Dragon 2 unveil, or, if those are unavailable, Apollo style couches of
canvas strung between bars (basically a lawn lounger) could be used. If NASA
handles it, NASA could have the emergency seating ready in just over a year and
probably for less than 300 million. If SpaceX handles it, they can send
somebody down to Walmart to buy them for $40 each.
My last line was tongue in cheek. However, it’s also
illustrative of my main point; we already have, except for a few easily
addressable details, manned emergency capability to ISS. The main barrier isn’t
technical, it’s ossified procedures coupled with lack of will. (Which is why
NASA’s current plan, if Soyuz becomes unavailable, is cry “abandon ship!” and
evacuate ISS – and they can’t even do that without Russian help (a ride down on
Soyuz) which they may not have access to if the reason for the access crisis is
political.)
If anyone can see any flaws in any of the above concept, please let
me know and I’ll attempt to address them.
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