As all teams continue to track a July 8 launch of STS-135, an important final milestone was reached this month with the final integrated launch and mission simulations (sims) with the Flight Crew and their Flight Control Team. Particularly, these sims gave the crews a chance to practice a modified Systems Abort-Once-Around abort, an abort procedure modified specifically because of Atlantis’s smaller-than-normal crew size.
STS-135 Crew Size limitations:
One of the unusual aspects of STS-135 is the smaller crew size. The STS-135 crew consists of Commander Chris Ferguson, Pilot Doug Hurley and Missions Specialists Sandy Magnus and Rex Walheim. The four-person crew size is driven by the need to assure their safe return to Earth in case something happens to Atlantis during the mission that prevents her from safely returning her crew to Earth.
The reason for the Soyuz crew return stems from the lack of a follow-on mission from STS-135/Atlantis that could be used to rescue the Atlantis crew in the event a Contingency Shuttle Crew Support (CSCS) was declared. Since STS-114 in July 2005, either a dedicate Space Shuttle mission or the next manifested Shuttle mission has been available to rescue the crew of a stranded orbiter.
However, unlike STS-134/Endeavour which was originally planned as the final Space Shuttle flight with a specially created rescue mission (STS-335), STS-135 will fly without a subsequent rescue or Launch-On-Need (LON) Space Shuttle since no additional Shuttle hardware, in the form of an External Tank and Solid Rocket Booster stack, exists.
In this manner, a hypothetical rescue situation for Atlantis’s crew would involve a complicated ISS crew rotation shuffle in which the Atlantis crew would bump the next four U.S. astronauts scheduled to launch to Station on the Russian Soyuz in order to take their return seats.
With this reduction in crew size, the STS-135 crew will still have to accomplish all of the mission’s nominal pre-docking activities – activities normally planned for seven or six people.
And while a four-person crew is not unprecedented as both STS-5 (Nov. 1982) and STS-6 (April 1983) flew with four-person crews, the complexity of Shuttle operations and flight plans has increased significantly in the almost 30-year period of time between then and now.
Particularly, STS-5 and STS-6 were primarily satellite deploy missions (the first ones in Shuttle history), with a long Flight Day 1 culminating in the first (or only) satellite deploy. Both missions were also planned to demonstrate the first Shuttle Extravehicular Activity (EVA) or “spacewalk” on Flight Day 4 with re-entry and landing on Flight Day 6.
Conversely, International Space Station (ISS) missions today generally retain a busy and short Flight Day 1, a pace that generally continues with orbiter Thermal Protection System (TPS) inspections and Station rendezvous preparations on Flight Day 2 and rendezvous and docking to the Station on Flight Day 3.
As previously documented by NASASpaceflight.com, STS-135 will feature a longer post-launch FD-1 (8.5hrs instead of the nominal 6.5hrs) and slightly delayed docking to the ISS in the FD-3 timeline: 1day 23hrs after liftoff v. the nominal 1day 19-21hrs after liftoff.
But the differences between STS-135 and previous missions don’t stop at crew size and mission timelines. In addition to the differences between Shuttle missions at the beginning of the program vs. now, there are also some differences in the more time-critical phases of flight, like Ascent and Entry.
During one of the last integrated simulations involving the a Space Shuttle flight crew and the flight control team, the training team scripted an ascent run designed to evaluate the teamwork involved in executing an abort case that would challenge the team resources and the four-person crew.
Particularly, a Systems Abort-Once-Around abort or Systems AOA, is one of the highly unlikely emergency scenarios that a crew and control team must be prepared to handle to ensure the best possible chance to return the crew and orbiter home safe and sound.
In general, AOA aborts tend to be based more on systems failures rather than a loss of performance, such as an early SSME (Space Shuttle Main Engine) shutdown. As Ascent Flight Director Richard Jones explained in an interview after the simulation: “To actually perform an AOA just based on trajectory/performance is very, very hard to do – it’s almost impossible.
“You almost require some sort of systems problem that says ‘come back home immediately,’ that didn’t require you to come back home immediately even beforehand, like on a TAL (Transoceanic Abort Landing) or RTLS (Return to Launch Site abort). That’s what [the AOA] abort case is designed for – to handle a late-breaking systems issue” that isn’t enough to mandate a TAL or RTLS but does mandate the immediate termination of the flight.
For Ascent and Entry, all four STS-135/Atlantis crew members will be seated (and busy) on the orbiter’s Flight Deck (FD). In some emergency scenarios, particularly during an aborted ascent, the MOD FRR presentation notes that there may be a lot of actions for the crew to take in a specific sequence and little time to get all that work done.
In the past, with larger crews, one or more crew members were always seated on the middeck and could more easily and quickly reach switches on that deck. This is simply not the case with STS-135.
Particularly, one of the MOD FRR presentations notes some of the procedural changes that resulted from the smaller crew as well as experience gained from the STS-135 training flow.
“Pending outcome of AEFTP [Ascent Entry Flight Techniques Panel] – PL POWERDOWNS – both Loss of 2 Freon Loops and Loss of 2 H2O Loops call for powerdown of all Middeck Payloads,” notes the Vehicle Division presentation to MOD FRR – available for download on L2.
The result of not powering down these middeck payloads will be greater heat generation then usually allowed for during a Systems AOA.
However, since the heat from these middeck payloads would be less than the heat normally generated by three additional astronauts seated down on the middeck, it was determined that simply letting these payloads remain active instead of putting added stress on the Flight Crew in a time-critical moment was more desirable.
Systems AOA Simulation – One of the last for the Shuttle Program:
Given its status as one of the last ascent/abort simulations in Space Shuttle Program history, members of the media were invited to observe two of the last planned integrated simulations on June 16 and 17.
During these simulations, the Ascent Flight Control Team practiced with the flight crew on the 16th followed by ISS rendezvous and docking practice with the Lead/Orbit 1 team and flight crew the 17th.
In the last ascent run on the 16th, the training team ran an ascent script intended to test the modified Systems AOA procedures.
For the ascent simulation, the flight crew was suited in their Launch and Entry suits in the Motion Based Shuttle Simulator in Building 5 at JSC (in yet another ‘last’, it was the last “suited” simulation at JSC).
During the simulation, the Systems AOA abort was primarily driven by the loss of one water loop and the degraded capability of the other. Shortly before Main Engine Cut Off (MECO), Electrical, Environmental and Consumables Engineer (EECOM) Mike Fitzpatrick reported that water loop 1 had failed with a leak and that water loop 2 was blocked.
The water loops on the actual orbiter are part of the vehicle’s cooling system and are critical in terms of keeping the orbiter’s avionics equipment operational. Without sufficient cooling, critical systems eventually overheat and fail.
After MECO, EECOM provided an initial assessment to the Flight Director. With water loop 1 unavailable and reduced water flow through loop 2, it became critical to return Atlantis to Earth after a single orbit (the ‘once around’ part of an AOA abort) and land while her critical electronics were still functioning.
Fitzpatrick was still initially assessing whether broader, more aggressive systems powerdowns would be necessary to keep a minimal number of critical systems alive during the Systems AOA.
STS-135 Specific Articles: http://www.nasaspaceflight.com/tag/sts-135/
Meanwhile, as the ascent simulations are typically designed to do, the Flight Control Team was also working a problem with External Tank separation when shortly after MECO, ET separation was inhibited.
The crew worked a procedure to manually close the ET LO2 (Liquid Oxygen) feedline disconnect valve and manually command ET separation – a procedure that proved successful about six minutes after MECO.
After ET separation was successfully completed, EECOM had the crew begin working an initial set of powerdowns, including two of the four primary General Purpose Computers (GPCs), to see if there was enough remaining cooling flow from water loop 2 to stay out of the Systems AOA case.
Meanwhile, Propulsion Systems Officer (PROP) Dean Lenort reported a large leak in the left OMS helium tank, which required both OMS burns to be executed with one set of OMS propellant tanks feeding both OMS engines.
The first OMS burn was performed 25 minutes after liftoff with the left-side tanks, with the plan to use the right-side tanks for the second burn: the deorbit burn.
Shortly after the first OMS burn, EECOM reported that the blockage on water loop 2 had gotten worse and that it looked like they would probably need to do a Systems AOA. There was still enough flow in the water loop to keep the communications system up and negate any middeck powerdown actions.0
At this point, Capsule Communicator (CapCom) Barry Wilmore relayed the information to the crew so they could get out the appropriate checklists and be ready to start executing procedures on Mission Control’s call.
However, before completely committing to the Systems AOA, Flight Director Jones tried one last time to see if there was any way to stay out of it. “And PROP, you can simplify our lives if we can avoid any of this. Same goes for you, EECOM – if we can stay out of the Sys AOA. Is there anything we can do to stay out of this book?”
After the simulation was over, Jones explained why the team hoped to avoid Sys AOA: “It’s just a big stresser. That is a contingency case in itself. You have to powerdown a lot of systems and accept a loss of redundancy in your systems just to make it through the power requirements that EECOM is requiring you to do.
“When you have loss of cooling, you can’t generate heat, and so in order to make up for that you just lose systems and you keep powering them down until you have the ability to handle the heat-removal capability.”
Back at the simulation, Jones then addressed the whole team on the big picture: “Folks we are 30 minutes away [from the deorbit burn]. We’re going to be using Target Set 4. We’re going to have to be very efficient.
“Guidance, as soon as we can, get the trajectory stuff out of the way – that way we can help the crew along the way for the right side of the room.”
A short time later, Jones updates his team on the situation. “OK folks, I’m going to need play-by-play from all of you. The crew is going to be working very hard. They’re going to be working individually just to get all the things done. So I’m going to need you to keep us in sync by saying where they are at.”
With the flight control team watching and monitoring their systems and calling out other needed actions, the flight crew worked through the checklist procedures to powerdown redundant equipment and prepare for the upcoming deorbit burn.
During this time, the flight control team was also able to identify some procedures that could be avoided after the burn to reduce the crew’s workload during re-entry.
The crew and flight controllers got the vehicle in a good power configuration and a good deorbit burn configuration. At this time, the simulation lead “called” the end of the sim run just before the burn would have started about 62 minutes after liftoff.
Following the simulation, the flight crew came to the control center to speak with the media. When asked about the modified Systems AOA scenario, Commander Chris Ferguson remarked, “That was a little different.
“I wasn’t expecting that, but it was extraordinarily well-scripted. We had to bring the motion down in the simulator so we could get people out of their seats so they could start throwing all the switches they needed to throw to do everything.
“It was very unusual to run through a scenario like that, but it’s very important we practice something (like that). We have a very small crew this time.
“We don’t have anyone on the middeck. I think it was a great script and gave us an opportunity – and the mission control team – an opportunity to see just what our capabilities are with regard to getting people out of their seats shortly after the main engines cut off and go through the multitude of switches we had to throw today.
“I think we left no switch unturned.”
When asked about whether the team had practiced a Systems AOA in an integrated simulation prior to this, Flight Director Jones said: “It is very, very rare for us to do a Systems AOA from a flight-specific, integrated (simulation) perspective.
“That (abort) is a very big stresser, but I think what we needed for this particular mission, for a four-person crew, was to investigate what our pinch-points are. This flight almost demands it.”
(Images: Via photos and video footage of the sim (L2) by Philip Sloss at JSC for NASASpaceflight.com. Crew shot by Larry Sullivan MaxQ Entertainment/NASASpaceflight.com. Further articles on STS-135′s status in work, driven by L2′s fast expanding STS-135 Special Section which is already into the FRR content and live flow coverage, plus more.
As with all recent missions, L2 is providing full exclusive level flow and mission coverage, available no where else on the internet. To join L2, click here: http://www.nasaspaceflight.com/l2/)