A Typical Morpheus Test Day
by Morpheus Ops Lean, Ian Young (@ICYprop)
Hey Morpheus fans! In this write-up I'll take you through a test day in a fair amount of detail. Most of you only get insight into the last 20 or so minutes when our Ustream feed goes live. Hopefully you'll enjoy this behind the scenes look into all the hard work the team puts in to make each flight happen.
As you probably expect test day is a busy day with many tasks to accomplish to get to ignition. The overall day can be broken up into several different sections, each of which I'll go over in more detail below. The different portions of the day are Safety Brief & Vehicle Rollout, Pre-Fill Checkout, Propellant Load (Liquid Oxygen and Liquid Methane), Leak Check, Final Preparation, Flight, and Post Test. A typical test day is about 10 hours from roll-out until Morpheus is back in the hangar. There are two teams working in tandem to get Morpheus ready for flight, the Pad Crew and Control Center. The Pad Crew is out at the pad and performs all the physical tasks needed to get ready for the test; this includes flipping switches and hooking up hoses. The Control Center operators monitor telemetry and send commands to Morpheus. (For more details on the various positions see the previous blog post)
The test day begins with the entire team meeting at Morpheus' hangar, where our PM goes over the plan for the day. The briefing starts by covering hazard and safety topics applicable for that day's test, such as cryogenics, pressure vessels, and laser firings. It's vitally important that in a contingency the entire team knows what actions need to be taken. After the safety brief is covered each discipline reviews changes or items of note for their subsystem, including giving their concurrence they are ready for flight. At this point the team is ready to get the test day underway.
The pad crew finalizes Morpheus for transport from the hangar to the pad area. Morpheus must then be transported from the south end of the Shuttle Landing Facility (SLF) to the north end. The 3 mile trek takes about 20 minutes to ensure Morpheus isn't jostled too much on the ride.
While Morpheus is on the way to the pad, the control team heads to the SLF air traffic tower where the control center is located. Here the operators begin configuring their consoles for the test day.
Once Morpheus arrives at the pad it is lifted off the cart by a crane and placed on launch stands. The three launch stands align with three load cells on Morpheus that allows the team to monitor the weight and center of gravity (c.g.) up until the moment of ignition. The launch stands fall away as Morpheus lifts off. Once on the launch stands, the pad crew then begins positioning all the ground equipment required to get Morpheus ready for flight, items such as grounding straps, propellant tankers, and ground power. When both the pad crew and control center teams are ready, the team powers on Morpheus' avionics and moves on to system checkouts.
Prior to loading propellants all of Morpheus' systems are checked out. This allows the team to work any issue that may come up before the cryogenic propellants are onboard. Most of the day Morpheus is powered by a ground power cart to preserve the onboard flight batteries. Once powered up the vehicle is precisely leveled on the launch stands using the onboard Inertial Measurement Unit (IMU). Being level helps ensure that when propellant is loaded it will settle out evenly between the two tanks.
Once level a process known as 'Gyrocomping' is kicked off. The gyrocomp initializes the accelerometers inside the IMU and must be performed any time the IMU is powered on. The process is about 3 minutes and internal to the IMU. During this time the vehicle must be as still as possible as the gyrocomp uses the sensed rotation of the Earth as part of its process.
After gyrocomp we checkout all the mechanical valves and actuators to ensure proper function. First, we test out the helium disconnect mechanism. Helium is used to pressurize the tanks to their flight pressure. A remote system is needed because the high tank pressures means the pad crew must be at least 1250 feet away. After a successful disconnect checkout we check all the other valves (which include vent valves, cooling valves, and engine valves) on Morpheus. This is a total of 16
We then move on to the actuator check. For this portion we put Morpheus on to flight batteries to ensure they can handle the power draw required to drive the actuators simultaneously. There are three elctro-magnetic actuators (EMA's) on Morpheus; one drives the throttle and the other two gimbal the engine. With those checks complete we command each of the four RCS jets valves open and to spark. Finally, we conclude this portion of checkouts with checking the main engine spark.
In parallel with the actuator checks we checkout two of the three ALHAT sensors, the Doppler Lidar and Laser Altimeter. These two sensors don't give very useful data until we're moving, so at this point we are mainly looking to ensure they booted up properly and that the temperatures are all nominal. When the actuator and ALHAT checkouts are complete we go back on to the ground battery cart.
To complete the functional checkouts we test the remaining ALHAT sensor, the Hazard Detection System (HDS), and the Thrust Termination System (TTS). The TTS's main function is to independently shutdown the main engine should the need arise. The TTS accomplishes this by shutting a valve on each of the propellant feed systems to the main engine. The TTS also has a function to stop the HDS laser from firing, thus providing an independent method to safe that part of the vehicle as well. The HDS system uses a laser that is not eye safe so extra precautions are taken by the team to ensure safety. With the HDS system powered, the full functionality of the TTS system is checked by verifying that it will also stop the HDS laser from firing.
The HDS is then pointed at two different targets to verify pointing accuracy of the system. Precisely pointing the HDS system is a key requirement for the ALHAT flights.
At the successful conclusion of the functional checkouts the team prepares to begin loading propellants on to Morpheus.
At this point the team is ready to load the Liquid Oxygen (LOX) and Liquid Methane (LCH4) on to Morpheus. Generally, we load LOX first but can, and have, loaded Methane first. During loading we fill to fairly precise quantities. Of course we don't want to run out of propellant during a flight, but we also don't want to overfill too much. Any propellant that we aren't planning to burn is simply dead weight that we have to carry with us. So you can see it's a fine balancing act. This is where it's very handy to have Morpheus resting on the three load cells; their weight readings are our best gas gauge.
Because the propellants are cryogenic, they will continue to boil off throughout the day and this must be accounted for by the Prop officer when setting the loading targets. When the propellants are first put into the tanks they boil off at a very high rate because the tanks are at ambient air temperature. Once the tanks chill down the boil off rate is very predictable. To help avoid some uncertainty, after the rapid boil off is finished we top the tanks back off to the target load. Once both propellants are loaded the team is really on the clock. If too much propellant is allowed to boiloff there won't be enough left to perform the day's test.
The final checkout that can only be performed once propellant is on board is a leak check. With cryogenic propellants on board, seals and fittings can shrink allowing propellant vapors to escape, so a leak check is performed. Valves are closed to stop the propellants from escaping as they boil off, and so that pressure can be built up in the tanks. With the pad crew safely back from the vehicle the tanks are pressurized up to 40 psi with helium. After a wait period, required personnel are allowed back to Morpheus to check for leaks and make final torques on the propellant systems. The leak check generally takes about 35 minutes to complete. For most on the team this is the final calm before the storm.
When leak check is complete the TTS is checked out one more time at cryogenic temperatures and then the pressure is released from the tanks to allow the propellants to cool back down. (The explanation for that phenomenon is for future blog post.) Morpheus and the team are now ready to make the final push to flight.
While the leak check was under way the pad crew was busy removing any unnecessary equipment and staging it for when the team retreats. The ground cooling of the avionics is disconnected, Morpheus is switched over to flight batteries, and the various on-board cameras are turned on. Finally, the valves are once again closed to allow for pressurization and the crew is ready to retreat from the pad area. Once the pad crew has safely retreated pressurization of the tanks begins. Pressurization takes about 20 minutes, and the flight pressures range from 300-355 psi, depending on the objectives of the day. As pressures come up we use some of the methane to cool Morpheus' electronics, and ALHAT is also configured for flight. Once at flight pressure the helium line is disconnected and retracted to a safe distance.
The team is now ready for the final Go/No-Go poll conducted by the Test Conductor (TC). With all systems "Go" and final words from the Flight Manager (FM), the final engine conditioning is performed. The command to start the onboard ignition sequence is sent. 5...4...3...2...1...
If you've seen the video then I think this section speaks for itself. (A future blog will detail what Morpheus and ALHAT are doing during the flight)
Once Morpheus is safely on the ground at the landing pad the control team executes the necessary commands to safe the vehicle systems prior to allowing the pad crew to head down range. This means venting leftover pressure, making sure there's no fires on the vehicle, and that the laser has stopped firing.
Once down range, the pad crew works to put Morpheus on stands, so the control team can get weight readings as propellant offload occurs. If need be, the pad crew will also hook up ground cooling and power.
Propellant off-load happens one commodity at a time to get an accurate reading of how much remained on board. This information helps to refine the engine model used to predict performance. Once offload is complete, Morpheus is rolled back to the hangar where the vehicle methane tanks are inerted for safety, post-flight inspections are completed, and high-rate data is offloaded in preparation for the next flight.