A United Launch Alliance Delta IV conducted a morning launch from Vandenberg Air Force Base on Wednesday, carrying a classified payload for the US National Reconnaissance Office. Liftoff of the NROL-65 mission, which deployed the last KH-11 reconnaissance satellite, occurred at 11:03 local time (16:03 UTC).

Delta IV-H Launch:

NRO Launch 65, or NROL-65, was the name given to the launch by the National Reconnaissance Office, who will operate the payload. Once it reaches orbit the satellite will be given a designation as part of the USA series – most likely USA-245.

NROL-65 was the 37th mission to fly with an NROL designation, a system which was introduced in late 1996 when the NRO began to publicly acknowledge its launches. The first NROL mission, NROL-2, was launched in December 1996 – for unknown reasons NROL-1 did not fly until 2004.

Like most NRO payloads, details about the NROL-65 spacecraft and its mission, including the type of satellite and its orbit, are classified. That said, the identities of many NRO satellites are open secrets and this mission is no exception.

NROL-65 was launched from the Vandenberg Air Force Base in California, a site typically used for launches to low Earth orbit – including the sun-synchronous orbits which optical imaging satellites operate in. Equatorial orbits, such as a geosynchronous orbit, are not accessible from Vandenberg.

The satellite was launched atop a Delta IV Heavy rocket – the most powerful rocket currently flying – and few payloads require a rocket of that size, especially to the orbits it can reach from Vandenberg.

The only NRO spacecraft launched to anything other than Low Earth orbit from Vandenberg in recent years are the two “Improved Trumpet” signals intelligence satellites flown in 2006 and 2008. The 2006 launch used a Delta IV Medium+(4,2), so an “Improved Trumpet” satellite would not require the Heavy’s payload capacity.

Several NRO payloads are currently operating in low Earth orbit; four KH-11 optical-imaging satellites, three Lacrosse and two FIA-R radar-imaging birds, several pairs of NOSS naval signals intelligence satellites and possibly USA-144 – the last Misty satellite which was launched in 1999, and was lost by amateur observers shortly after launch. NOSS and FIA-R, like “Improved Trumpet” are too small to require a Delta IV Heavy, leaving three possibilities for the identity of the payload.

The Misty program was reported to have been cancelled in the mid-2000s due to its exceptionally high cost, and no such satellite has been launched in over 14 years. Lacrosse is currently in the process of being replaced by FIA-R, so it is unlikely that another launch would occur at this late stage in the program.

Notices to Airmen, or NOTAMs, issued for the launch to ensure that aircraft do not stray into the path of the rocket, show that the rocket will fly south-southwest from Vandenberg on a heading consistent with the approximately 98 degree orbit occupied by KH-11 satellites. Close to the scheduled launch time, one of the constellation’s two operational planes will intersect the launch site.

The KH-11 is the last in a long line of Keyhole optical imaging satellites, which began with the KH-1 Corona in 1959.

NROL-20, launched in 2005, was expected to be the last KH-11 satellite, however two additional satellites were reportedly procured as gap-fillers after the system’s replacement was delayed. The first of this pair of satellites, USA-224 or NROL-49, was launched in early 2011, so NROL-65 will be the final KH-11, and the last of the Keyholes, marking the end of an era in US satellite reconnaissance.

The Keyhole program began with a series of technology demonstration satellites. Discoverer 1, launched in February 1959 by a Thor DM-18 Agena-A, would have tested the spacecraft’s communications systems, however it failed to achieve orbit.

The next two missions attempted to test a film return capsule to allow satellites to physically return the photos they took to Earth, in an era before digital photography. While the US did experiment with scanning images in orbit and transmitting them during the Samos program of the same era, the quality and reliability of the images was found to be insufficient.

Discoverer 2, the first of these two satellites, ejected its capsule prematurely. The vehicle reentered over the Arctic and was not recovered – its fate has been reported to have been the inspiration for the novel and film Ice Station Zebra. Discoverer 3 failed to orbit. The film return capsules were deorbited by means of a Star-12 solid rocket motor.

The first KH-1 reconnaissance satellite was Discoverer 4, which failed to orbit. Of the ten KH-1 satellites, four were lost in launch failures and five of the spacecraft which were launched successfully failed to return any images.

After Discoverer 11 failed, two more demonstration launches without film occurred, with Discoverer 13’s capsule becoming the first object to be successfully recovered from orbit. KH-1 launches resumed, with Discoverer 14 flying the first, and only successful mission.

The final mission, Discoverer 15 was successful up until recovery of the film capsule was attempted – the planned airborne capture of the vehicle failed. Despite being designed for a back-up recovery from the ocean, the spacecraft sank before it could be retrieved.

The KH-1 was replaced by the KH-2, or Corona Prime. Unlike the Agena-A-derived KH-1, the KH-2 was based on the Agena-B, boosted by a Thor DM-21 first stage, however it made use of the same film-return capsules, or SRVs. Six KH-2s reached orbit successfully out of ten attempts between October 1960 and November 1961.

The KH-3, or Corona Triple Prime which replaced it used the same bus but with the C”’ camera rather than the C’ used on the KH-2. A short-lived program, only six were launched with the last failing to achieve orbit.

The KH-3 was replaced by the KH-4 Corona-M, or Mural. This consisted of two cameras, based on the C”’, mounted 30 degrees apart to enable spectroscopic images to be produced. Initially the same Agena-B-based bus as the KH-2 and 3 was used, however a few months into the programme the more capable Agena-D was introduced.

In total eleven Agena-B and fifteen Agena-D-based KH-4s were launched between 1962 and 1963, mostly boosted by Thor DM-21 rockets, however a small number used the Thrust-Augmented Thor SLV-2A.

In 1963 the KH-4 design was modified with the addition of a second SRV, and the Mural camera was replaced with a pair of J-1s and a lower-resolution wide-angle camera for area mapping. Named the KH-4A or Corona-J, these spacecraft were launched by the Thrust-Augmented Thor SLV-2A Agena-D (TAT Agena-D), and later the Thorad SLV-2G Agena-D.

The Thorad-Agena was derived from the Thor-Agena, but with the Long Tank Thor first stage developed for the Delta program in place of the standard Thor used on previous Agena launches. The Thorad’s full designation was the Long Tank Thrust Augmented Thor, or LTTAT. In all, fifty two KH-4A spacecraft flew, the last in 1969.

The last series of KH-4-based satellites were the KH-4Bs, which carried J-3 cameras and an improved area survey payload, the Dual Improved Stellar Index Camera or DISIC. Seventeen launches used Thorad-Agena rockets, in both the SLV-2G and SLV-2H configurations, with the last occurring in May 1972.

Prior to the area survey cameras being fitted to KH-4A and B satellites, dedicated spacecraft were used for this mission. Named the KH-5, or Argon, twelve were launched between 1961 and 1964. For the first seven launches, the KH-5 was based on the Agena-B, boosted by a Thor DM-21. From the eighth launch onwards the Agena-D was used, with the Thrust-Augmented Thor SLV-2A boosting the last three.

The KH-6, or Lanyard, was a short-lived attempt to fly a higher-resolution camera developed for the Samos program aboard a KH-4 film-return capsule. The program was abandoned after three missions in 1963, only one of which was completed successfully – the first satellite failed to orbit, and the second failed to feed film into the camera, resulting in no images being returned.

Lanyard was replaced by the KH-7, also known as Gambit or Project 206. The KH-7 was initially launched by the Atlas LV-3 Agena, and later the Atlas SLV-3 Agena, however unlike previous Keyhole satellites the Agena did not form part of the spacecraft. A total of 38 spacecraft were launched, with 36 reaching orbit, before the KH-7 was replaced by the KH-8, or Gambit-3.

Fifty four KH-8 satellites were launched, across four development blocks. Due to their size the more powerful Titan rocket was used to place them into orbit, with the first twenty four missions using the standard Titan IIIB, which was then replaced with the Titan III(23)B. From the thirty-second launch onwards, the stretched Titan III(24)B was used. All of these rockets consisted of two-stage Titan vehicles, derived from the Titan II, with an Agena-D third stage.

The fifty-second KH-8 was placed into a much higher orbit than standard KH-8 satellites. Since the program’s declassification it has emerged that the spacecraft, designated the “Dual Mode” mission and also known as “Higher Boy”, was built as an interim satellite to provide area reconnaissance following the retirement of the KH-4B, however a mapping payload was instead added to the KH-9 satellites, allowing them to assume this role.

The KH-8 satellite was not required and was later repurposed for a higher-orbit reconnaissance mission in 1982 – ten years after the last KH-4B mission.

The KH-9, which was also known as Hexagon, was the last film-return Keyhole satellite. Twenty were launched, with all but the last reaching orbit successfully. Most launches used the Titan III(23)D rocket, however the last three flew on the Titan III(34)D. Each satellite carried four Mark 8 SRVs, descendants of those used on the earlier missions, with several missions carrying a fifth SRV, a Mark five, to support an additional area mapping payload mounted at the front of the satellite.

Throughout the Keyhole program, many secondary payloads have been flown – both on the satellites themselves and on the rockets. From the late KH-4 satellites onwards, “Hitchhiker” electronic intelligence (ELINT) payloads became common and by the KH-9, most launches carried at least one. Such secondary payloads have not been deployed on KH-11 launches.

Keyhole film capsules were designed for aerial recovery, with a C-119 Flying Boxcar or C-130 Hercules aircraft snaring the spacecraft’s parachutes as it descended. In theory the capsules could also be recovered from the water should the aircraft capture them, however on some flights they sank before this could be accomplished.

There was no KH-10 satellite; the designation was applied to the Dorian imaging payload planned for the Manned Orbiting Laboratory, however that program was cancelled before any functional spacecraft were launched.

Unlike its predecessors, the KH-11 or Kennen did away with film-return capsules – instead it transmits images to the ground electronically. This allowed US intelligence agencies much faster access to the images since they did not need to wait for the next film capsule to return.

Additionally, since the satellites’ operational lifespan was no longer limited by the number of film capsules they carried, they were able to operate for far longer than any previous Keyhole satellites had. The longest-lived KH-11, USA-129, has been in service for almost 17 years; the longest Hexagon mission lasted nine months.

The first KH-11 was OPS 5705; launched by a Titan III(23)D from Space Launch Complex 4E at Vandenberg on 19 December 1976. It ended its 25-month mission with reentry in January 1979. A second satellite, OPS 4515, was launched in June 1978 and operated until August 1981.

These two satellites operated in what observers now designate the west plane of the KH-11 constellation; the launch of OPS 2581 in February 1980 targeted a new plane, with approximately the same apogee, perigee and inclination, but a different ascending node time, causing the satellite to pass over different parts of the world at different times of day.

After OPS 2581, launches mostly alternated between the east and west planes; with the next satellite – OPS 3984 – going into the West plane to replace OPS 4515 in September 1981, just days after its predecessor was deorbited. In the east plane OPS 2581 was deorbited in late October 1984, with OPS 9627 launching to replace it in mid-November. OPS 3984 was deorbited in November 1984 and OPS 9627 in August 1985.

It is believed that there have been four generations, or blocks, or KH-11 satellites. The first five spacecraft were Block I satellites, and were operated in orbits with 500 kilometers apogee, 200-300 kilometers perigee and around 97 degrees inclination.

With the Titan III(23)D replaced by the Titan III(34)D, or Titan 34D, heavier satellites could be launched and to higher orbits, allowing the Block II KH-11 to replace the Block I. Four Block II satellites were launched, the first was placed into the west plane in December 1984 under the designation USA-6.

From USA-6 onwards, the apogee of the satellites’ orbits was increased, typically to between 800-1000 kilometers. In order to keep the orbits sun-synchronous, the inclination was increased to around 98 degrees. The longest-serving Block II satellite, USA-6 remained in service for almost a decade – finally being deorbited in November 1994.

The first Block II satellite launched for the east plane fared less well. Following a first stage engine failure 213 seconds after launch, the vehicle began went out of control. Following a loss of thrust in the other engine shortly afterwards, followed by a premature stage separation, the vehicle was destroyed by range safety. As a result of the failure, the next launch also went to the east plane, deploying USA-27 in October 1987. This satellite operated until June 1992.

The fourth and final Block II spacecraft was launched in November 1988, into the west plane. Designated USA-33, it remained in service until May 1996.

Block III satellites were originally designed to be deployed from the Space Shuttle, which would have flown deployment missions from Space Launch Complex 6 at Vandenberg – the same pad which the Delta IV flew from with NROL-65.

Following the Challenger accident in January 1986, missions from Vandenberg were deemed too risky and cancelled.

The Titan IV rocket was developed to launch the military payloads which the Shuttle had been expected to deploy, including the new-generation KH-11s.

The increased payload capacity of the Titan IV compared to the 34D allowed the satellites to carry more fuel – extending their operational lives still further. The first Block III spacecraft, USA-86, was launched in November 1992, into the East plane, where it operated for seven and a half years.

The next launch also flew to the east plane, with USA-116 taking over duties as the primary satellite and USA-86 becoming its backup. Launched in December 1995, USA-116 was deorbited in November 2008, after almost thirteen years in service.

The third Block III satellite, USA-129, was launched into the west plane on 20 December 1996. The first satellite whose launch was publicly acknowledged by the NRO and announced in advance, it was also designated NROL-2. Almost seventeen years old, it remains in service as a backup to USA-186.

The next satellite to launch, USA-161 or NROL-14, has been identified by some observers as a Block IV satellite due to slight differences in its appearance and operation. It marked another change in rocket for the KH-11; switching from the Titan IV(404)A to the Titan IV(404)B. The launch took place in October 2001, with the satellite operating in the east plane.

Like USA-139 it appears to remain in service as a backup, however when it was replaced it was moved into a near-circular orbit at an altitude of 390 kilometers – unusually low for a KH-11.

USA-186, or NROL-20, was intended to be the last KH-11 satellite. Generally considered to be a Block III spacecraft, it was the payload of the final Titan launch in October 2005. It has been speculated that USA-186 may be somewhat different to its predecessors, since the Titan IV that carried it had a shorter payload fairing than those used for previous KH-11s. USA-186 is currently in service as the primary satellite in the west plane.

The primary satellite in the east plane is USA-224; the satellite launched as NROL-49 by the Delta IV Heavy which flew from Vandenberg in January 2011. USA-224 has been identified as a Block IV satellite, however it was built some time after USA-161 – having been put together along with NROL-65 to fill a gap between the aging KH-11s in orbit and the stalled development of their successors.

NROL-65 was the sixteenth KH-11 to launch. In addition to the fifteen KH-11 satellites which have been launched to date, two Misty satellites, USA-53 and USA-144 (NROL-9), were launched in 1990 and 1999 respectively; the former was deployed from Space Shuttle Atlantis during STS-36, and the latter was orbited by a Titan IVB.

Misty, which was derived from the KH-11, operated in a lower-inclination orbit of around 65 degrees. The Titan IV which launched USA-144 used the same, shorter, payload fairing used on the rocket which deployed USA-186, leading to some initial speculation before USA-186’s launch that the spacecraft could be a third Misty.

Designed for low-observability, both Misty satellites released decoys to make it appear that they had failed in orbit before raising their orbits. USA-144 deployed an additional, inflatable, decoy into a much higher orbit which successfully confused amateur observers. Amateur observers watching NRO satellites were occasionally able to track USA-53, which appears to have been deorbited in 1997, however there has never been a confirmed sighting of USA-144.

The KH-11 was to have been replaced by the optical component of the Future Imagery Architecture program. Conjecturally known as “FIA-O” and “FIA-R”, Future Imagery Architecture satellites would have replaced the KH-11 optical imaging, and Lacrosse radar-imaging satellites respectively.

The first FIA-R was launched as USA-215, or NROL-41, in 2010; however the optical component of the program was cancelled around 2005, with the project severely over budget and behind schedule.

A launch contract signed with International Launch Services – who at the time operated the Atlas V rocket – called for the launch of the NROL-29 payload in mid-2007. It has been speculated that NROL-29 would have been the first FIA-O satellite, with the launch disappearing from schedules around the time of FIA-O’s cancellation.

Lockheed Martin was awarded a contract for initial development of a new class of electrooptical satellite in 2009. Named Next-Generation Electro Optical, or NGEO, this satellite will likely enter service in the mid 2010s, replacing the KH-11.

The mission patch for NROL-65 shows an American eagle, with hands instead of wings, holding the world in its right hand and a snake in the left. The snake’s tail forms the lower-case Greek letter omega – the last letter of the Greek alphabet, an omega symbol has featured on many patches where the rocket or payload has been making its final flight.

The Eagle has a tattoo on its left arm with the inscription “Buttercup” and is wearing a khaki jacket emblazoned with the US flag and a badge reading “DYS”. The patch bears the inscription “Sheachadadh Do Rudai”: “deliver your stuff” in Gaelic, presumably relating to the “DYS” on the Eagle’s uniform.

The launch patch shows the vehicle “flying into the sunset”, however it is unclear whether the launch patch would contain imagery related to the payload’s identity. If it does contain such imagery, the groups of three, three and two stars on that patch could represent the three old-generation radar imaging satellites still in service, the three KH-11s which will be in the west plane after this launch, and the two currently in the East plane.

For this launch the rocket was named Victoria – the previous KH-11 was launched by a rocket which had been named Betty.

Victoria was the fifth Delta IV to launch from Vandenberg, and the second Heavy. Overall, it was the twenty-fourth Delta IV to fly and the seventh use of the Heavy configuration. First flown in 2002, the Delta IV is one of two Evolved Expendable Launch Vehicles (EELVs) in the US launch fleet, along with the Atlas V.

Both the Atlas V and Delta IV are operated by United Launch Alliance, a company formed in 2006 to provide EELV and Delta II launches to the US government. The launch of NROL-65 will be the seventy-fourth launch conducted by ULA – the seventeenth Delta IV since launch operations were transferred from Boeing.

The Delta IV is almost exclusively used for US military launches; four commercial missions were conducted earlier in the program – the maiden flight carried a Eutelsat spacecraft and three commercial delivery-in-orbit contracts for the National Oceanic and Atmospheric Administration’s GOES-N, O and P satellites were inherited from the Delta III rocket after the Delta III was retired due to poor reliability.

The only other non-military launch currently contracted to the Delta IV is for NASA’s Exploration Flight Test 1 mission – the maiden flight of the Orion spacecraft – which is scheduled for next year.

In addition to its four commercial launches, the Delta IV has deployed two DSCS and four WGS communications satellites, one DSP missile defense satellite, three Global Positioning System navigation satellites, seven classified NRO payloads and the HLV-OLSSP demonstration payload; the latter being launched, along with a pair of university nanosatellites, on the first test flight of the Delta IV Heavy.

That launch ended in the only launch failure of the Delta IV to date – cavitation in the first stage and booster oxidiser lines led to both boosters and the first stage cutting out prematurely. HLV-OLDSP was placed into a much lower orbit than had been planned, while the nanosatellites failed to achieve orbit.

The seven NRO payloads on previous Delta IV launches have been identified a molniya-orbit ELINT satellite known as “Improved Trumpet” by observers; three geosynchronous ELINT, or Mentor, satellites; an SDS communications satellite and an FIA-R radar-imaging spacecraft.

It is unclear whether one of the geosynchronous ELINT satellites, NROL-15 or USA-237, may have represented the first of a new-generation of satellites, an “Improved Mentor”, as it used an upgraded Delta IV Heavy rocket with RS-68A engines.

The RS-68A was not be used on the NROL-65 mission; Victoria, or Delta 364, used standard RS-68-powered Common Booster Cores (CBCs). The CBC is used as the first stage of all Delta IV configurations; powered by a single engine, it burns liquid hydrogen propellant, with liquid oxygen used as an oxidiser. In the Delta IV Heavy, two additional CBCs are used as boosters, strapped to either side of the first stage.

The second stage was a five-meter Delta Cryogenic Second Stage (DCSS), powered by an RL10-B-2 engine, which uses the same propellants as the first stage. The rocket is rounded out by a five-meter composite payload fairing, which encapsulates the satellite.

Details of the mission profile which Victoria flew have not been published; however it is likely that a similar profile was used to that flown by Betty in 2011. It had already been confirmed that ignition of the starboard CBC’s engine would occur two seconds earlier than on previous launches – at T-7 seconds rather than T-5 – to try to mitigate a fireball effect noted on previous launches.

The effect – caused by the rocket’s exhaust igniting hydrogen vented near the rocket – has scorched or even set fire to the first stage insulation on previous flights. While it has been observed on launches from both Vandenberg and Cape Canaveral, the effect is more severe on west-coast launches.

The port and core CBCs ignited at the usual time of T-5 seconds, with all three engines building up to launch thrust by T-0, when Victoria was released to begin her ascent to low Earth orbit. The rocket cleared the tower after about seven seconds and initially ascended vertically before pitching-over to fly downrange.

The core CBC was throttled down around 45 seconds after liftoff. Around 80 seconds after launch Victoria passed through the area of maximum dynamic pressure, followed a few seconds later by the rocket passing through Mach 1.

The outboard CBCs began throttling down a little before four minutes after launch, with cutoff and separation occurring about ten seconds after throttle-down.

Once the boosters separated, the core stage throttled up to full thrust.

The engine burned at full thrust until around five minutes and twenty seconds after liftoff, when it will began to throttle down again, this time in preparation for its own cutoff; MECO, or main engine cutoff, which occurred around eight seconds after the throttle-down command is given.

About ten seconds after cutoff, the first stage was jettisoned, with the DCSS deploying its extendable nozzle and beginning its prestart sequence. Second stage ignition came around 12 seconds after staging. Approximately twenty-two seconds into second stage flight, the payload fairing separated from the vehicle.

At this point, all official coverage of the launch ended, except for a statement confirming whether the satellite successfully reached orbit – which has on some previous missions been released before the launch has even been completed. This statement was released around 75 minutes after launch.

The second stage is likely to make a single burn, lasting in excess of 12 minutes, before spacecraft separation. While literature values for a Delta IV Heavy mission to low Earth orbit suggest a second, 19-second, burn would be made around 71 minutes after the end of the first, a second set of NOTAMS for the launch suggest that the DCSS will be deorbited into the Pacific ocean of the west coast of California on its first orbit, which would put spacecraft separation much earlier in the flight than with the two-burn profile.

Victoria was the ninth rocket to launch from Space Launch Complex 6 (SLC-6) at Vandenberg Air Force Base.

Built in the late 1960s to support Titan IIIC launches in support of the Manned Orbiting Laboratory (MOL) program, the complex was left unused after MOL was cancelled. During the early 1980s it was rebuilt as a Space Shuttle launch complex, however again this was cancelled before a single rocket had been launched from the complex.

SLC-6 was finally used for a launch in August 1995, when a rocket named the Lockheed Launch Vehicle launched the GEMStar-1 communications satellite. The complex’s bad luck continued, however, as the rocket failed to achieve orbit. By the time of the next launch, Lockheed had merged with Martin Marietta, and the rocket had been renamed the Lockheed Martin Launch Vehicle. Despite a successful launch the payload, NASA’s Lewis satellite, failed after only three days in orbit.

The third launch from SLC-6 was made by an Athena II – a derivative of the Lockheed Martin Launch Vehicle which had since been renamed again, and was known as the Athena I. The rocket’s payload fairing failed to separate, resulting in the loss of the Ikonos satellite on board. A second Ikonos launch, in September 1999, was successful however it marked the final Athena launch from SLC-6.

During the early 2000s, the launch complex was rebuilt for the Delta IV. Two launches in 2006 carried NROL-22 – an “Improved Trumpet” ELINT satellite, and a DMSP weather satellite respectively, before the pad was closed to allow its modification to support the Delta IV Heavy.

Click here for NROL News Article: http://www.nasaspaceflight.com/?s=NROL

Since the NRO’s large low Earth orbit reconnaissance satellites were expected to have been replaced by the smaller FIA spacecraft, it was not anticipated that heavy-lift launches would need to be made from the west coast and the complex had to be modified ahead of NROL-49.

The NROL-49 launch was conducted successfully in 2011. The next year, a Delta IV Medium+(5,2) orbited an FIA-R satellite, NROL-25, from the pad. With no more KH-11 launches expected, NROL-65 could well be the last Delta IV Heavy to fly from Vandenberg.

Wednesday’s launch was the eleventh to be conducted by the United States so far this year; the eighth for United Launch Alliance, and the third for the Delta IV. It was the second Delta IV to launch this month, following the mission from Cape Canaveral, using the Medium+(5,4) configuration, which deployed a Wideband Global Satcom satellite on 8 August.

The launch began a busy month for America’s rockets, with Minotaur, Falcon, Antares and Atlas launches all scheduled in the next four weeks. The first of these, the Minotaur V’s maiden flight carrying NASA’s LADEE spacecraft bound for the Moon, is scheduled for 6 September.

The next Delta IV launch is currently expected on 17 October, from Cape Canaveral with a GPS navigation satellite. The next NRO Launch, NROL-39, is scheduled for December aboard an Atlas V 501; that payload is most likely an FIA-R radar imaging satellite.

(Images via ULA, L2 Historical and Public Domain).