WorldView-2 launched via Delta II out of VAFB

by William Graham

DigitalGlobe’s WorldView-2 satellite has been launched atop a United Launch Alliance Delta II rocket on Thursday morning. The launch, which took place from Vandenberg Air Force Base in California, USA at 11:51 (local) – slightly delayed from the scheduled T-0 due to a battery issue on the vehicle’s second stage.

Launch Preview:

The WorldView-2 spacecraft is an optical imaging satellite, which will be operated by Colorado-based DigitalGlobe. It was constructed by Ball Aerospace, and is based on the BCP-5000 satellite bus. It has a mass of 2,800 kilograms, and an anticipated operational lifespan of seven and a quarter years.

It will be the second BCP-5000 satellite to be launched, following the earlier WorldView-1 satellite in 2007. DigitalGlobe advertise the satellite as having the “highest resolution available commercially” – via a camera with an aperture of 110 centimetres, and is capable of producing images in eight spectral bands; red, green, blue, yellow, near-infrared, “red edge”, “coastal”, and “near-infrared 2”.

WorldView-2 is the fifth satellite to be launched for DigitalGlobe, which was founded in 1993 as the WorldView Imaging Corporation. In 1995 it merged with the remote sensing division of Ball Aerospace to form EarthWatch Incorporated. Its first satellite, EarlyBird-1, was launched in December 1997, however its power system failed four days after launch and the satellite was declared a total loss.

A second satellite, QuickBird-1, was lost in a launch failure in November 2000, followed by Quickbird-2 – which was successfully launched in October 2001. In 2002 EarthWatch was renamed DigitalGlobe, and in September 2007 WorldView-1 was launched on a Delta II.

Thursday’s flight will use Delta 345, the three hundred and forty fifth Delta family rocket to be launched. It will fly in the Delta II 7920-10C configuration, which consists of an Extra-Extended Long Tank Thor first stage, augmented at liftoff by six GEM 40 solid rocket motors, with a further three GEM 40 motors igniting later in the flight.

The first stage is fuelled by RP-1, with liquid oxygen being used as an oxidiser. The second stage will be a Delta-K, which will complete the ascent, placing the satellite into orbit. It burns Aerozine-50 propellent in dinitrogen tetroxide oxidiser. A 3-metre (10-foot) diameter composite payload faring will encapsulate the spacecraft during its ascent through the atmosphere.

The first stage is powered by an RS-27A main engine, with two vernier engines for roll control, all of which will ignite around two seconds before liftoff. At liftoff, the six ground-lit GEM 40 motors will also ignite, and Delta 345 will be released to begin its climb to orbit. Just under thirty three seconds after launch, the rocket will pass through Mach 1, the speed of sound, and about forty eight seconds after launch it will be subjected to maximum dynamic pressure, or max-Q.

Sixty four seconds into the flight, the six solid motors which ignited at launch will burn out, with the three air lit motors igniting one and a half seconds later. The spent motors will remain attached for a further 20.5 seconds in order to avoid debris hitting an oil rig, before separating in two groups of three, one second apart. Ninety seconds into the flight, Delta 345 will yaw to begin a dog-leg manoeuvre in order to adjust the orbital inclination of its destination. The manoeuvre will last fifty two seconds.

Around two minutes and ten seconds into the launch, the air-lit motors will burn out, and about two seconds later they will separate. The first stage will then power Delta 345’s ascent until its fuel is depleted. This is scheduled to occur four minutes and thirty one seconds into the flight, at which time the first stage main engine will shut down, an event known as MECO. The two verniers will follow suit shortly afterwards, at an event which is known as VECO.

Eight seconds after MECO, the first and second stages will separate, with the second stage’s AJ-10-118K engine igniting five and a half seconds after staging. Four second stage burns are planned for Delta 345, with two occurring prior to spacecraft separation, and the remaining two occurring afterwards.

Around four seconds after the second stage ignites, the payload fairing will separate. This event is scheduled to occur at a point when the rate of free molecular heating on the vehicle falls below 1,135 watts per square metre, or 0.1 British thermal units per square foot per second. The first burn of the second stage will conclude with cutoff, or SECO-1, ten minutes and fifty two seconds after launch. Delta 345 and its payload will be in an orbit of 195 by 805 kilometres (106 by 435 nautical miles), inclined at 98.6 degrees.

Following SECO-1, Delta 345 will manoeuvre to its coast attitude, and a thermal conditioning, or “barbecue” roll will be initiated, with the upper stage rotating at a rate of two degrees per second. Midway through the coast phase, the direction of the roll will be reversed. Shortly before the second burn is initiated, the roll manoeuvre will be terminated, and the rocket will realign to the necessary attitude for the burn. Ignition will occur fifty three minutes and twenty four seconds into the flight.

The second burn will last twenty two seconds, ending with SECO-2. This will leave Delta 345 in a parking orbit of 764 by 776 kilometres (413 by 419 nautical miles). The burn will not affect inclination. Following SECO-2, the vehicle will reorient for spacecraft separation, and then begin a spin-up roll manoeuvre, to a rate of nine degrees per second. Sixty one minutes and forty seconds after liftoff, WorldView-2 will separate from the carrier rocket.

After the spacecraft has separated, the second stage will perform a series of evasive manoeuvres and burns. Ten minutes after separation, the rocket will perform a twenty-five second cold gas evasive manoeuvre. Just under eighteen minutes later, the second stage will make its third burn, which is scheduled to last five seconds. Eight minutes and fifteen seconds after SECO-3, the fourth burn will begin. This will be the depletion burn, and is scheduled to last around fifty two seconds.

Vandenberg Air Force Base’s Space Launch Complex 2W will be used for today’s launch. The pad, which was originally designated 75-1-2, was built for use by Thor missiles attached to the 75th Strategic Missile Squadron of the United States Air Force. The first launch from the pad occured on 17 September 1959, and was conducted by the British Royal Air Force.

In 1962, the first orbital launch from the complex occurred, when a Thor-Agena placed a KH-4 reconnaissance satellite into orbit. The first launch of a Delta from SLC-2W occurred in 1969, and in 1995 the Delta II began using the complex. It is currently designated as the launch site for all but one of the remaining Delta II launches.

Today’s launch is the 146th flight of the Delta II. The next Delta II launch is scheduled to occur on 7 December, with the WISE satellite for NASA. Before that, a Delta IV is scheduled to launch on 19 November, with the WGS-3 military communications satellite. The next launch for United Launch Alliance is currently planned to be an Atlas V with a DMSP military weather satellite, on 18 October.

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