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.
Overview
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)
Safety Brief &
Rollout
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.
Pre-Fill Checkout
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 valves. 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.
Propellant Load
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.
Leak Check
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.
Final Preparation
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…
Flight
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)
Post Test
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.