A lot has happened since the last post, leading up today, where the rocket and payload were buttoned up and on the rail, undergoing final checkouts in preparation for tomorrow’s Flight Readiness Review and “Dress Rehersal” (also know as a practice countdown).
On Jan 14th (about a week ago), electronics connections in the experiment section were completed in preparation for the Sequence Test (more on that below). In addition, a successful test of how timing information from the on-board Global Positioning System (GPS) receiver on-board the rocket payload is incorporated into the science telemetry data was lead by Slagle, Carruth, and Frank Waters (NSROC). The science team requested and designed this additional test because having accurate timing information for the rocket data will be crucial in making the comparisons with the ground-based imager data after the flight. Knowing more about how the on-board timing system works helps with post-flight check out and verification of the timing.
for this test, the payload remained safe and sound inside the Payload Assembly Building (PAB), while the GPS signal was cabled down to it from an antenna located on the roof of the PAB. Later in the week the payload will be “buttoned up”, i.e. all the skirts and the nose cone installed, and it will be rolled out for – wait for it – the Rollout Test, where the payload uses it’s own GPS antenna to receive the signals and do the navigation.
The data from this test generated significant discussion and analysis between Slagle, Carruth, Christian Amey, and Jim Diehl (both NSROC), with many kilobytes of text and megabytes of data traversing a variety of e-mail Inboxes. Resolution came down to good old sketches on paper and phone conversations, for which the Science team is grateful!
On Wed, 15 Jan 2014, the long-awaited Sequence Test occurred, and was successful!
Why a Sequence Test? A rocket flight is a carefully planned and choreographed series of events, starting even before launch (“T minus 0”) and proceeding through the 10-20 minutes of the flight in a way that maximizes the chances of successful boost to altitude and collection of scientific data through the flight. Just about all of these events (1st stage ignition; 1st stage separation; 2nd stage ignition; …; nose cone ejection; reorientation of the payload; boom releases; high-voltage turn on for the particle instruments; etc.) occur on cue from electrical timers in the body of the rocket and payload.
the Sequence Test starts and runs all those timers in a safe and controlled environment, with a variety of electrical test equipment standing in for things like rocket motor igniters, pyros (see below), and power supply switches. By running this sort of a test, the science and engineering teams can tell if the timers are programmed correctly, and that all the electrical signals happen at the right time, on the right wires, with the right amount of power to ignite the motor, fire the pyro, or throw the relay that allows the instrument to turn on completely and make its measurements.
Sequence Tests are just one of the many “test as you fly” activities the science and engineering teams do to get the rocket and payload ready for the flight. Other examples would be:
– vibrating the payload and making sure it still works afterwards, simulating the strong gee forces experienced during the thrust phase of the flight when the motors are burning (“Vibe Testing”).
– running science data from the sensors all the way through the entire signal processing, radio transmission and reception, and ground data processing chain to make sure that what goes in comes out (“TM Tests”, “End-To-End Testing”).
– rehearsing the electrical, mechanical, and most of all personnel operations that lead up to the launch to make sure everyone knows what, how, and when to do their part of the operation to make sure that when the aurora are right, it all comes together (“Sequence Tests”, “Dress Rehersal”).
In each case, the teams run through a practice that’s as near to the real thing as feasible to uncover faults and issues with either the hardware, software, or operating procedures (how things get done, and in what order), diagnose them, correct them, and move on to the next with confidence.
On Thu, 16 Jan 2014, all the final mechanical adjustments, installations, removals of safeties, and installation of pyrotechnic devices (pyros) on the payload occured. This included the pin and clips that keep the Fields Quad Stacer Booms from accidentally deploying on the ground, and so at this point, the payload is mechanically “live”, although for any of the booms to actually deploy, power from the TM section would have to be applied.
The use of explosive devices like pyros to release doors, springs, booms, and other mechanisms on rockets has a long and successful history. Any time one has something that needs to be held strongly during the time when the rocket motors are burning (and vibrating the payload at significant gees!), but then released to allow the science payload to conduct measurements, some sort of mechanical fastener that is cut by a pyro is involved.
It’s only within the last ten years or so that non-pyrotechnic devices have been developed, and more importantly demonstrated their reliability, and have then found their way onto sounding rockets and spacecraft, taking up the role of pyros. These devices usually use a material known as a shape-memory alloy (SMA), typically wound in coils or as long “tendons” or “muscles”. The SMA material starts with one shape or length, and then when heated, usually by passing electrical current through it (think of the coils in a toaster), it changes shape, pushing specially-designed bolts to their breaking point, or pulling on small mechanisms connected to the ends of the fibers, and thus releasing booms from their restraints, opening or closing small doors over particle detectors, etc.
The forward and aft “skirts” which cover all of the aft science instruments and most of the forward instruments were installed, as was the nose cone, buttoning up the payload:
Fin bolt story here? “for the want of a nail…”
The GREECE PI, Marilia Samara arrived on 16 Jan 2014 as well, and immediately dove into preparations for both the payload and the ground imagers. Michell, Grubbs, and Samara having closed up the MEPS, APES, and APIS particle detectors (LINK TO GREECE – The Instrument), worked long hours with Don Hampton (UAF GI) to get the multiple imagers and their shelters ready for the trip to Venetie, AK.
Friday and Saturday, 17-18 Jan 2014 found the NSROC team completing all the mechanical tasks on the payload prior to the Rollout Test scheduled for Mon, 20 Jan 2014.
In addition the NSROC team “staged both of the rocket motors that make up the GREC rocket to the launch rail and started work on the insulating “box” that will surround the rocket while it is exposed on the launcher. The box allows heaters to pump warm air around the entire payload and keep the rocket motors and instruments at safe temperatures regardless of how cold it gets waiting for the aurora to cooperate!
On Monday, 20 Jan 2014, Michell and Hampton headed out in a single-engine chartered prop plane for Venetie, AK along with the ground imagers essential for the GREECE mission. Venetie is a village of just over 200 people located about 159 mi (256 km) NNW of Fairbanks, AK, and this is the second season where Venetie has hosted the SwRI imagers.
The payload team worked on the Roll Out test on Monday as well. Here the experiment payload is wrapped carefully in blankets and rolled out side the Payload Assembly Building so that it’s telemetry antenna can be seen by the receiving antennas up the hill at the Telemetry (TM) site, and its GPS antennas can see the transmissions from the satellites in the GPS constellation:
- GREECE payload in cradle with electrical umbilicals outside of Payload Assembly Building for Rollout Test
Turn-On test, a.k.a. the Boom Test?
John Bonnell, Co-I for Fields from UCB arrived the evening of 20 Jan 2014 as well.