Screenshot from ULA Webcast of the OCO-2 launch. Standing in the spotlight waiting for the fog
Mission Rundown: ULA - Delta II 7320-10C - OCO-2
Written: January 26, 2023
A sigh is just a sigh - Not anymore
NASA’s Orbiting Carbon Observatory completed its ride to orbit on Wednesday morning, launched atop a United Launch Alliance Delta II rocket, following a 24 hour turnaround.
A defective solenoid valve that prevented water flow into the sound suppression system caused the scrub seconds ahead of yesterday's launch attempt.
Liftoff took place from Space Launch Complex 2 West at the Vandenberg Air Force Base in California was right on schedule Wednesday July 2, 2014 at 02:56 PDT - 09:56 UTC.
The OCO-2 Payload
Orbiting Carbon Observatory 2, or OCO-2, is a near-identical replacement for its ill-fated predecessor. Constructed by Orbital Sciences Corporation around the LEOStar-2 bus, the satellite has a mass of 454 kilograms (999 lb). Of this 45 kilograms (99 lb) is propellant.
OCO-2 Satellite (Graphic image credit: NASA JPL)
The small satellite is designed for a two-year mission, however NASA hopes to be able to operate it for longer. End of mission is September 2023 over nine years later.
OCO-2 uses a three axis stabilized LeoStar-2 bus, consisting of a 2.12 m long hexagonal column 0.94 m wide, with a launch mass of 449 kg. The bus contains the ACS (Attitude Control Subsystem) module, consisting of four reaction wheels, star trackers, a MIMU (Miniature Inertial Measurement Unit), 13 sun sensors and a magnetometer.
The LeoStar-2 bus also carries a 96 Gigabit solid state recorder for onboard data storage, both science and housekeeping data is downlinked using an L3 Communications X-band transmitter and a body-mounted X-band patch antenna, at a data rate of 150 Mbit/s.
Two ~900 Watt GaAs solar panels will be used to generate electricity to power the single Eagle Picher 35 Ah NiH (Nickel-Hydrogen) battery in the spacecraft.
Destined for a sun-synchronous orbit, OCO-2 will join the A-Train, or Afternoon Train, a constellation of Earth-observing satellites which fly in formation to complement each other’s observations. The “Train” consists of the Earth Science Satellites Aqua, Aura, CALIPSO, CloudSat and Shizuku (GCOM-W1).
The primary objective of the OCO-2 mission is to study the absorption of sunlight by carbon dioxide atoms in the atmosphere. To this end, the satellite is equipped with a single scientific instrument which will use three spectrometers to study the near-infrared spectra of light reflected from the surface of the Earth.
Absorption lines in the spectral images produced by the instrument can be used to determine areas of carbon dioxide and molecular oxygen in the regions studied.
Each of the three spectrometers is optimized for a particular wavelength of light. One will observe a region around 2.06 micrometers (microns) for a strong absorption band associated with atmospheric carbon dioxide.
The second will study a region of the spectrum around 1.61 micrometers in order to search for a weaker absorption band associated with carbon dioxide surface sources.
The third spectrometer is keyed to a wavelength of 0.765 micrometers, looking for absorption due to oxygen molecules which will be used to calibrate the results for the carbon dioxide data.
The OCO-2 satellite was originally manifested to fly atop a Taurus rocket, in the same configuration that its predecessor had used. Orbital Sciences attempted to resolve the issue which had led to the loss of OCO-1, and in March 2011 the rocket carried NASA’s Glory satellite on its return-to-flight mission.
After suffering the same fairing anomaly as befell OCO-1, NASA lost confidence in the Taurus requiring that it be recertified before entrusting further payloads to it.
NASA meanwhile re-awarded the OCO-2 contract to United Launch Alliance, using the proven Delta II rocket. Statistically the most reliable rocket currently in service, the Delta II last suffered a launch failure in early 1997 and has achieved 96 consecutive successful missions since.
The Delta II 7320-10C launch
The launch took place from Space Launch Complex 2 West (SLC-2W) at the Vandenberg Air Force Base in California. Built in the late 1950s, SLC-2W was originally part of the much larger Launch Complex 75.
The rocket that launched OCO-2 was Delta 367. Its first stage, the Extra-Extended Long Tank Thor, was powered by a single RS-27A engine with two vector adjustable Vernier motors to provide roll control. It uses RP-1 propellant with liquid oxygen as an oxidiser.
Ignition of the RS-27 occurred three seconds before the planned launch. At T-0, the three solid rocket motors ignited and Delta 367 began its ascent towards space. The rocket reached the speed of sound, Mach 1, in 35.7 seconds, passing through the area of maximum dynamic pressure – Max-Q – fourteen seconds later at 50 seconds.
A minute and four seconds into its flight, the Delta’s solid rocket motors burned out, having consumed their supply of propellant. Separation of the spent boosters did not occur for another thirty five seconds as the rocket first needed to clear an offshore oil field in order to ensure the jettisoned SRMs didn't fall on the oil rigs located there.
The first stage ended its burn with Main Engine Cutoff, or MECO, four minutes and 24.2 seconds after launch. Vernier Engine Cutoff, or VECO, followed shortly afterwards, with the spent stage separating eight seconds after burnout. Ignition of the second stage engine took place five and a half seconds after staging.
The second stage of Delta 367 is a Delta-K, which is powered by an AJ10-118K engine, burning Aerozine-50 propellant oxidized by dinitrogen tetroxide. The stage can be restarted, allowing multiple burns to ensure accurate orbital insertion.
On this mission two burns were conducted prior to spacecraft separation. The first lasted five minutes and 42.8 seconds, before a fifty-minute and 28.5 second coast phase began. Separation of the payload fairing occurred 23.3 seconds into the first burn.
The second burn lasted just twelve seconds, circularizing the vehicle’s trajectory for spacecraft separation.
The planned sun-synchronous deployment orbit is near-circular, with an altitude of 686 by 698 kilometers (426 x 434 miles or 370 x 377 nautical miles).
It will be inclined at 98.2 degrees, with a semimajor axis of 7,071 kilometers (4,394 miles, 3818 nautical miles), eccentricity of 0.0013 and an argument of perigee of 69.1 degrees. Spacecraft separation took place over the Indian Ocean off the East coast of Africa and close to the equator, at fifty-six minutes and fifteen seconds mission elapsed time; five minutes and 12.6 seconds after the end of powered flight.
Following spacecraft separation, the upper stage will perform two further burns to remove itself from the spacecraft’s operational orbit. The first of these will begin twenty eight and three-quarter minutes after separation and last 38.5 seconds.
The second, thirty-one minutes and 1.5 seconds later will be for about 50.9 seconds. As a result of these burns, the second stage is expected to end up in a 2,380 by 10,336 kilometer (1,478 by 6,423 statute miles or 1,285 by 5,581 nautical miles) orbit.
The reason why the second stage Delta K didn’t deorbit itself remains unclear, there must have been a second clandestine payload, an unknown mission objective or test program included in this NASA rocket launch.
The Delta II 7320-10C rocket
The launch will overall be the 152nd launch of the Delta II and the 129th flight for the 7000-series configuration, but not including the six Delta II Heavy missions.
The Delta II Heavy, or 7920H/7925H which appends an H to the designation to indicate the use of the more powerful GEM-46 solid rocket motors. Fittings and release mechanism at the base and sides of the Core are welded in to attach the GEM-46 strap-on motors.
The 7000 rocket to be used for today's launch was originally built as a Delta II Heavy core, but was converted back to a standard Delta II configuration to meet payload and launch site requirements. Some refitting, welding and assembly required.
Delta II split in its major parts. This is a 7420-10C configuration used in the ICESat-2 mission
For Delta II rockets the four digit number after the rocket’s name denotes the configuration it will fly in; for the launch it is a Delta II 7320. The first digit gives the type of first stage and booster rockets being employed, in this case an Extra-Extended Long Tank Thor augmented by three GEM-40 strap-on motors.
The second digit of the designation gives the number of solid rocket motors. For the Delta II this is either three, four or nine GEM-40 strap-on motors.
The third digit denotes the type of second stage being flown – for the Delta II this is always a Delta-K, denoted by the digit 2.
Finally, the fourth number is the type of third stage being flown; 0 for no third stage, 5 for a Star-48B or 6 for a Star-37FM. The OCO-2 launch will fly with three solid rocket motors and no third stage.
The payload fairing which encapsulates the OCO-2 satellite was a three-meter (10-foot) composite structure. The largest fairing used by the Delta II, its presence is denoted by adding “-10C” to the rocket’s configuration number.
The full classification of today's launch of Delta 367 is Delta II 7320-10C.
Delta II 7320-10C stands 58.90 meters - 127.6 feet tall. - Diameter 2.44 meter - 8 feet
Delta II 7320-10C weighs 151 700 kilo - 334400 pounds fully fueled and loaded
Delta II 7320-10C first stage weighs less than 20 000 kilo - 44 000 pounds when empty
Thor first stage RS-27 engine provides 3 020 kilonewton - 678 920 lbf of thrust
ATK GEM-40 height 12.96 meter - 42.51 feet - Diameter 1.02 meter - 3.34 feet
ATK GEM-40 weighs 13 064 kilo - 28 801 pounds at launch
ATK GEM-40 weighs 1 361 kilo - 3 000 pounds at jettison - 63 second burn time
ATK GEM-40 provides 499.2 kilonewton 112 225 lbf of thrust if ignited at altitude
ATK GEM-40 provides 446.0 kilonewton 100 264 lbf of thrust at sea level
