On February 1st, 2003, the seven crew members of the Space Shuttle Columbia perished when the shuttle disintegrated upon reentry into Earth's atmosphere. But is there a way that NASA could have rescued the crew while the shuttle was still in orbit?
Mere seconds after Columbia's launch on January 16th, 2003, a block of foam from the shuttle's external tank and struck Columbia's left wing, and likely created a 6-to-10-inch diameter hole in the wing. In the wake of the Columbia disaster, a Columbia Accident Investigation Board (CAIB) was formed to investigate all aspects of the mission. Their final report included the section "STS-107 In-Flight Options Assessment," which provides a possible rescue-and-repair scenario for the shuttle and her crew. At Ars Technica, Lee Hutchinson provides a narrative frame for this scenario, suggesting an alternate universe in which NASA launched an ambitious mission to rescue the crew. A rescue mission might have been possible for one key reason: at the time, the shuttle Atlantis was being prepped for its scheduled March launch. But there were a number of issues to consider; for example, ensuring that the astronauts didn't inhale deadly levels of carbon dioxide:
But even before those decisions could be made, NASA had to make another assessment—how long did it have to mount a rescue? In tallying Columbia's supplies, NASA mission planners realized that the most pressing supply issue for the astronauts wasn't running out of something like air or water but accumulating too much of something: carbon dioxide.
Weight is a precious commodity for spacecraft. Every gram of mass that must be boosted up into orbit must be paid for with fuel, and adding fuel adds weight that must also be paid for in more fuel (this spiral of mass-begets-fuel-begets-mass is often referred to as the tyranny of the rocket equation). Rather than carrying up spare "air," spacecraft launch with a mostly fixed volume of internal air, which they recycle by adding back component gasses. The space shuttle carries supplies of liquid oxygen and liquid nitrogen, which are turned into gas and cycled into the cabin's air to maintain a 78 percent nitrogen/21 percent oxygen mixture, similar to Earth's atmosphere. The crew exhales carbon dioxide, though, and that carbon dioxide must be removed from the air.
To do this, the shuttle's air is filtered through canisters filled with lithium hydroxide (LiOH), which attaches to carbon dioxide molecules to form lithium carbonate crystals (Li2CO3), thus sequestering the toxic carbon dioxide. These canisters are limited-use items, each containing a certain quantity of lithium hydroxide; Columbia was equipped with 69 of them.
How long those 69 canisters would last proved difficult to estimate, though, because there isn't a lot of hard data on how much carbon dioxide the human body can tolerate in microgravity. Standard mission operation rules dictate that the mission be aborted if CO2 levels rise above a partial pressure of 15 mmHg (about two percent of the cabin air's volume), and mission planners believed they could stretch Columbia's LiOH canister supply to cover a total of 30 days of mission time without breaking that CO2 threshold. However, doing so would require the crew to spend 12 hours of each day doing as little as possible—sleeping, resting, and doing everything they could to keep their metabolic rates low.
This plan wasn't on hand at the time the mission went into contingency mode; it was developed in the months following the tragedy. But could it have worked? A STS engineer chimes in in the comments:
I worked on the planning for the STS-125 rescue mission, STS-400. It took 18 months of planning to develop the procedures, modify the tools, test and simulate the GN&C, EVA, and robotics choreography, and prepare all the paperwork to satisfy everyone that it was a safe plan for both orbiters and the crew. The proposed plan in this article would have been even more difficult because there was no opportunity to use the RMS (robotic arm) to grapple Columbia. Columbia wasn't carrying an arm, and Columbia itself did not have a grapple fixture that Atlantis's arm could use. I am extremely dubious that the manual station keeping would be doable even just from a propellant standpoint: STS-400 had the crew transfer requiring two days. (The STS-400 timeline is available online) For Columbia, that would mean manually station-keeping for an entire EVA (6.5 hours), then separating until the next EVA is ready, and performing another rendezvous and station keeping for > 6.5 hours. I don't think there is anywhere near enough RCS fuel to do that.
The only hope that this plan would have ever had would have been if the plan had already been in place prior to Columbia's launch, as there is no way on this Earth that NASA would have approved a flight with untested procedures that could destroy both orbiters. As I said above, the very similar STS-400 flight planning took 18 months; even if the entire NASA work force worked around the clock, that amount of work wasn't going to happen in just a few weeks. Sadly, I can't see a path where this would have actually been feasible.
Be sure to read the entire piece at Ars Technica. It's fascinating to consider the work that would go into such a rescue mission, even if it was not able to help the Columbia crew.
Columbia Memorial photo taken by the US Navy, via Wikimedia Commons.