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Orbiting Vehicle or OV, originally designated SATAR (SATellite - Atmospheric Research), comprised five disparate series of standardized American satellites operated by the US Air Force, launched between 1965 and 1971. Forty seven satellites were built, of which forty three were launched and thirty seven reached orbit. With the exception of the OV3 series and OV4-3, they were launched as secondary payloads, using excess space on other missions. This resulted in extremely low launch costs and short proposal-to-orbit times. Typically, OV satellites carried scientific and/or technological experiments, 184 being successfully orbited through the lifespan of the program.
The first OV series, designated OV1, was built by General Dynamics and carried on suborbital Atlas missile tests; the satellites subsequently placed themselves into orbit by means of an Altair-2 kick motor. The Northrop-built OV2 satellites were built using parts left over following the cancellation of the Advanced Research Environmental Test Satellite; three OV2 spacecraft flew on Titan IIIC test flights. Space General built the OV3 satellites, the only series to be launched on dedicated rockets; six were launched on Scout-B rockets between 1966 and 1967. OV4 satellites were launched as part of a test flight for the Manned Orbiting Laboratory (MOL), with two satellites conducting a communications experiment whilst a third, OV4-3, was the primary payload, a boilerplate mockup of the MOL space station. Two further OV4 satellites, duplicates of the first two, were built but not launched. OV5 satellites were launched as secondary payloads on Titan IIIC rockets as part of the Environmental Research Satellite program.
The OV program was phased out in the late 1960s, the last of the series (an OV1) flying in 1971. It was succeeded by the Space Test Program, which focused on tailored satellites with specific payloads rather than standardized ones.
Program origin
The Orbiting Vehicle satellite program arose from a US Air Force initiative, begun in the early 1960s, to reduce the expense of space research. Through this initiative, satellites would be standardized to improve reliability and cost-efficiency, and where possible, they would fly on test vehicles or be piggybacked with other satellites. In 1961, the Air Force Office of Aerospace Research (OAR) created the Aerospace Research Support Program (ARSP) to request satellite research proposals and choose mission experiments. The USAF Space and Missiles Organization created their own analog of the ARSP called the Space Experiments Support Program (SESP), which sponsored a greater proportion of technological experiments than the ARSP.[1]: 417 Five distinct OV series of standardized satellites were developed under the auspices of these agencies.[1]: 425
Summary of launches
| Series | Contractor | First launch | Last launch | Built | Launched | Failed to orbit |
|---|---|---|---|---|---|---|
| OV1 | General Dynamics | 1965-01-21 | 1971-08-07 | 23 | 23 | 4 |
| OV2 | Northrop | 1965-10-15 | 1968-09-26 | 5 | 3 | 0 |
| OV3 | Space General AFRCL |
1967-04-22 | 1967-12-04 | 6 | 6 | 1 |
| OV4 | US Air Force Martin Marietta |
1966-11-03 | 1966-11-03 | 5 | 3 | 0 |
| OV5 | TRW Systems AFRCL Northrop |
1967-04-28 | 1969-05-23 | 9 | 8 | 1 |
OV1
Background
The OV1 series was an evolution of the 2.7 m "Scientific Passenger Pods" (SPP), which, starting on 2 October 1961, rode piggyback on suborbital Atlas missile tests and conducted scientific experiments during their short time in space. General Dynamics received a $2 million contract on 13 September 1963 to build a new version of the SPP (called the Atlas Retained Structure (ARS)) that would carry a self-orbiting satellite. Once the Atlas missile and ARS reached apogee, the satellite inside would be deployed and thrust itself into orbit. In addition to the orbital SPP, General Dynamics would create six of these satellites, each to be 3.66 m (12.0 ft) long with a diameter of .762 m (2 ft 6.0 in), able to carry a 136 kg (300 lb) payload into a circular 805 km (500 mi) orbit.
Dubbed "Satellite for Aerospace Research" (SATAR), the series of satellites was originally to be launched from the Eastern Test Range on Atlas missions testing experimental Advanced Ballistic Re-Entry System (ABRES) nosecones. However, in 1964, the Air Force transferred ABRES launches to the Western Test Range causing a year's delay for the program. Moreover, because WTR launches would be into polar orbit as opposed to the low-inclination orbits typical of ETR launches, less mass could be lofted into orbit using the same thrust, and the mass of the SATAR satellites had to be reduced.[1]: 417
Spacecraft
The standard OV1 satellite, 1.387 m (4 ft 6.6 in) long and .69 m (2 ft 3 in) in diameter, consisted of a cylindrical experiment housing capped with flattened cones on both ends[2] containing 5000 solar cells producing 22 watts of power. Two .46 m (1 ft 6 in) antennae for transmitting telemetry and receiving commands extended from the sides of the spacecraft. 12 helium-pressurized hydrogen peroxide thrusters provided attitude control. Starting with OV1-7, the solar cells were flat rather than rounded, and the satellites carried the Vertistat attitude system that used a Sun sensor to determine the spacecraft's orientation to the Sun.[1]: 418–429 OV1-13 and OV1-14 were the first in the OV1 series to use Pulse-code modulation digital telemetry, which afforded the return of more and more precise data from the satellites.[3]
Operations
Ultimately, only the first of the SATARs, (OV1-1, called Atmospheric Research Vehicle (ARV) at the time)[4]: 24 ever flew piggyback on an ABRES mission. The rest were flown on ex-ICBM Atlas D and F boosters specifically purchased by the OAR for the OV1 series (except OV1-6, which flew on the Manned Orbiting Laboratory test flight on 2 November 1966).[1]: 418–422 Typically, the satellites were mounted in the nose cone of the launching rocket; OV1-1, OV1-3 and OV1-86 were side mounted. A jettisonable propulsion module with an Altair 2 solid-propellant motor provided the thrust for final orbital insertion.
The OV1/Atlas combination was economical for the time, costing just $1.25 million per launch ($4545 per 1 kg (2.2 lb) of payload). The standardized format also afforded a quick experiment proposal-to-launch period of just fifteen months.[1]: 418 The program was managed by Lt. Col. Clyde Northcott, Jr.[5]
Significant results
Data from OV1-4's Tissue Equivalent Ionization Chamber, compared to a similar instrument orbited on Gemini 4, determined the radiation dose Gemini astronauts traveling at OV1-4's altitude (~950 km (590 mi)) would receive: 4 rads per day at a 30° inclination orbit or 1.5 rads per day at a 90° (polar) inclination orbit.[6]
In late May 1967, during a period of high solar and magnetic activity, OV1-9 returned the first evidence of Earth's long theorized but never measured electric field. The satellite detected a stream of protons flowing out of the atmosphere into space moving at more than 60,000 km (37,000 mi) per second. OV1-9 also studied the variation of proton fluxes in the outer Van Allen Belt during that same period, determining that fluxes were ten times greater four days after May's maximum solar activity than they had been before the flare; it took ten days for the fluxes to return to normal levels.[7] The X-ray spectrometer on the co-launched OV1-10 returned the most comprehensive set of solar X-ray observations to date. These data enabled scientists to determine the relative density of neon to magnesium in the solar corona through direct observation rather than using complicated mathematical models. The ratio of neon to magnesium was found to be 1.47 to 1 (+/- .38).[8]
OV1-13, launched 6 April 1968, measured increases in energy and intensity of electrons during a geomagnetic storm that took place 10 June 1968.[9] OV1-13 data also clarified how the particle flow caused by solar storms created these high altitude increases.[10]
Data returned by OV1s 15 and 16 returned the first substantial set of data on the density of Earth's atmosphere between the altitudes of 100 km (62 mi) and 200 km (120 mi) and proved that increased solar activity increased the air density at high altitudes, contradicting the prevailing model of the time. [11] Moreover, the satellites determined that the density of the upper atmosphere was 10% lower than predicted by theoretical models.[12] OV1-15/16 data led to improved atmospheric models that allowed the Air Force to better predict where and when satellites would decay and reenter.[11]
OV1 Missions
| Name | Mass | COSPAR ID | Launch | Reentry | Remarks |
|---|---|---|---|---|---|
| OV1-1 | 45 kg (99 lb),[4]: 24 86 kg (190 lb) with Altair booster[13] | 21 Jan 1965[14] | Geophysics; first westward launch of a satellite; orbited, but on-board Altair failed to fire.[4]: 24 | ||
| OV1-2 | 86 kg (190 lb) with Altair booster[13] | 1965 078A | 5 Oct 1965[14] | Radiation studies[15] | |
| OV1-3 | 92 kg (203 lb)[13] | 27 May 1965[14] | Biomedical radiation studies; Atlas failed two minutes into flight.[1]: 419 | ||
| OV1-4 | 87.6 kg (193 lb) | 1966 025A | 30 Mar 1966 | Thermal control experiments | |
| OV1-5 | 114.3 kg (252 lb) | 1966 025B | 30 Mar 1966 | Optical radiation test | |
| OV1-6 | 202 kg | 1966 099C | 3 Nov 1966 | 31 Dec 1966 | Inflatable decoy |
| OV1-7 | 117 kg | 14 Jul 1966 | 14 Jul 1966 | Sky science; failed to orbit | |
| OV1-8 | 3.2 kg | 1966 063A | 14 Jul 1966 | 4 Jan 1978 | Passive comsat open aluminum sphere |
| OV1-9 | 104 kg | 1966 111A | 11 Dec 1966 | Radiation studies; discovered Earth's electric field | |
| OV1-10 | 130 kg | 1966 111B | 11 Dec 1966 | 30 Nov 2002 | Radiation studies; studied solar X-rays and Earth's airglow |
| OV1-11 | 134 kg | 27 July 1967 | 27 July 1967 | Failed to orbit | |
| OV1-12 | 140 kg | 1966 072D | 27 July 1967 | 22 Jul 1980 | Radiation studies; also known as Flare Activated Radio-biological Observatory (Faro) |
| OV1-86 | 105 kg | 1966 072A | 27 July 1967 | 22 Feb 1972 | Cosmic ray telescope; Earth's heat radiation |
| OV1-13 | 107 kg | 1968 026A | 6 Apr 1968 | High altitude radiation studies | |
| OV1-14 | 101 kg | 1968 026B | 6 Apr 1968 | EM interference, radiation studies, and Lyman Alpha solar astronomy | |
| OV1-15 | 213 kg | 1968 059A | 11 July 1968 | 6 Nov 1968 | Air density, solar studies; also known as Solar Perturbation of Atmospheric Density Experiments Satellite (Spades) |
| OV1-16 | 272 kg | 1968 059B | 11 July 1968 | 19 Aug 1968 | Ionospheric drag experiment; also known as Cannonball-1 |
| OV1-17 | 142 kg | 1969 025A | 18 Mar 1969 | 5 Mar 1970 | Solar studies |
| OV1-17A | 221 kg | 1969 025D | 18 Mar 1969 | 24 Mar 1969 | Ionospheric studies; also known as Orbis Cal-2 |
| OV1-18 | 1969 025B | 18 Mar 1969 | 27 Aug 1972 | Ionospheric studies | |
| OV1-19 | 1969 025C | 18 Mar 1969 | Radiation studies | ||
| OV1-20 | 1971 061A | 7 Aug 1971 | 28 Aug 1971 | Radar calibration, radiation studies | |
| OV1-21 | 1971 061B | 7 Aug 1971 | Radar calibration, air density studies |
OV2
Background
The OV2 series of satellites was originally designed as part of the ARENTS (Advanced Research Environmental Test Satellite) program, intended to obtain supporting data for the Vela satellites, which monitored the Earth for violations of the 1963 Partial Test Ban Treaty. Upon the cancellation of ARENTS due to delays in the Centaur rocket stage, the program's hardware (developed by General Dynamics) was repurposed to fly on the Titan III[1]: 417 : 422 (initially the A,[18] ultimately the C) booster test launches.[1] The USAF contracted Northrop to produce these satellites, with William C. Armstrong of Northrop Space Laboratories serving as the program manager.[18]
Spacecraft
The OV2 satellites were all designed on the same plan, roughly cubical structures of aluminum honeycomb, .61 m (2.0 ft) in height, and .58 m (1.9 ft) wide, with four 2.3 m (7.5 ft) paddle-like solar panels mounted at the four upper corners, each with 20,160 solar cells. The power system, which included NiCd batteries for night-time operations, provided 63 W of power. Experiments were generally mounted outside the cube while satellite systems, including tape recorder, command receiver, and PAM/FM/FM telemetry system, were installed inside. Four small solid rocket motors spun, one on each paddle, were designed to spin the OV2 satellites upon reaching orbit, providing gyroscopic stability. Cold-gas jets maintained this stability, receiving information on the satellite's alignment with respect to the Sun via an onboard solar aspect sensor, and with respect to the local magnetic field via two onboard fluxgate magnetometers. A damper kept the satellites from precessing (wobbling around its spin axis). Passive thermal control kept the satellites from overheating.[1]: 422
Operations
Three OV2 satellites with different mission objectives were originally planned when the OV2 program began.[18] The OV2 series was ultimately expanded to five satellites, all with different goals. Only OV2-5, a radiation and astronomical satellite, achieved a degree of success.[19]
Significant results
OV2-5 proton energy data collected 2–13 October 1968 in the energy range of 0.060 to 3.3 Mev, showed an eight-fold reduction in particle flux between solar storms and quiet periods. Measuring the angle at which protons encountered the satellite also helped refine theoretical models of how the magnetosphere interacts with the flux of charged particles.[20]