RADCAL
{{Short description|Radar calibration satellite}}
{{Infobox spaceflight
| name = RADCAL
| image = RADCAL.jpg
| image_caption = Manufacturer photograph of RADCAL
| mission_type = Radar calibration
| operator = United States Air Force
| COSPAR_ID = 1993-041A
| launch_date = {{start-date|23:30:00 UTC on 25 June 1993|timezone=yes}} UTC
| launch_rocket = Scout S217C
| launch_site = Vandenberg SLC-5
| SATCAT = 22698
| mission_duration = 3 year (design life)
| declared = 2013
| launch_mass = {{convert|89.3|kg}}
| orbit_reference = Geocentric
| orbit_regime = Low Earth
| orbit_periapsis = {{convert|791|km|mi}}
| orbit_apoapsis = {{convert|9000|km|mi}}
| orbit_inclination = 89.5 degrees
| orbit_period = 101.40 minutes
| orbit_eccentricity = 0.00754
| apsis = gee
}}
RADCAL (short for RADar CALibration Satellite) was a radar calibration satellite launched and operated by the United States Air Force. It was active from June 1993 until it stopped communicating in May 2013.
Design
= Construction =
RADCAL was built by Defense Systems Inc. as United States Air Force Space Test Program payload P92-1. It was built under a one-year contract-to-launch{{cite web |last1=Krebs |first1=Gunter D. |title=RadCal (P92-1) |url=https://space.skyrocket.de/doc_sdat/radcal.htm |website=Gunter's Space Page |access-date=20 October 2021 |language=en}} and cost $10 million.
= Components =
Payload included two C Band transponders (operating at the same frequency as space-detection radars), a Doppler beacon that transmitted at 150 and 400 MHz, and a pair of modified Trimble Inc. TANS Quadrex Global Positioning System receivers. The receivers were used to determine the satellite's orbit as a reference for calibrating space detection radars. It also carried the Small Satellite Power System Regulator, an experiment testing improved battery charging on solar panel-equipped vehicles.{{cite book |last1=Kramer |first1=Herbert J. |title=Observation of the Earth and Its Environment: Survey of Missions and Sensors |date=30 January 2019 |publisher=Springer |isbn=978-3-642-56294-5 |page=1102 |url=https://books.google.com/books?id=T2W-DwAAQBAJ |access-date=21 October 2021 |language=en}}{{cite news |title=New Satellite to Improve Radar Tracking of Spacecraft, Planes, Missiles With PM-Space Shuttle |url=https://apnews.com/article/327927233d7f9e55f40641dd64978c57 |access-date=20 October 2021 |work=AP News |date=26 June 1993}}
Mission
= Launch =
RADCAL launched into polar orbit at 23:30:00 UTC on 25 June 1993{{cite web |title=NASA - NSSDCA - Spacecraft - Telemetry Details |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1993-041A |website=nssdc.gsfc.nasa.gov |access-date=20 October 2021}} from Vandenberg Air Force Base's Space Launch Complex 5. The launch vehicle was Scout S217C.{{cite web |last1=McDowell |first1=Jonathan |title=Jonathan's Space Report No. 159 |url=http://www.planet4589.org/space/jsr/back/news.159.txt |website=Jonathan's Space Report |access-date=20 October 2021}}
= Operation =
RADCAL was used to calibrate ground-based space tracking radars: they would track it and compare their estimated position to its true position. By the end of its operational lifetime, it was one of only two functional radar performance monitoring satellites (along with DMSP F-15) and was actively used by a number of civilian and military organizations.{{cite journal |last1=Martin |first1=Larry |last2=Fisher |first2=Nicholas |last3=Jones |first3=Windell |last4=Furumo |first4=John |last5=Heong |first5=James Ah Jr. |last6=Umeda |first6=Monica |last7=Shiroma |first7=Wayne |title=Ho'oponopono: A Radar Calibration CubeSat |journal=Small Satellite Conference |date=9 August 2011 |url=https://digitalcommons.usu.edu/smallsat/2011/all2011/42/ |access-date=21 October 2021}} Its GPS receivers were used in experiments to determine its attitude in space.{{Cite journal| doi = 10.1002/sat.4600120504| issn = 1099-1247| volume = 12| issue = 5| pages = 427–433| last1 = Cohen| first1 = Clark E.| last2 = Lightsey| first2 = E. Glenn| last3 = Parkinson| first3 = Bradford W.| last4 = Feess| first4 = William A.| title = Space flight tests of attitude determination using GPS| journal = International Journal of Satellite Communications| accessdate = 2021-10-21| date = 1994| url = http://onlinelibrary.wiley.com/doi/abs/10.1002/sat.4600120504| url-access = subscription}} It was the first satellite to use a GPS to determine its attitude.{{cite web |title=RADCAL |url=https://cddis.nasa.gov/926/egm96/radcal.html |website=cddis.nasa.gov |access-date=21 October 2021}} RADCAL was designed to last for three years, but remained operational until May 2013.{{cite web |last1=Lawrence |first1=Taylor |title=Satellite |url=https://www.kirtland.af.mil/News/Article-Display/Article/817968/satellites-operation-time-exceeds-expectations/ |website=Kirtland Air Force Base |publisher=377th Air Base Wing Public Affairs |access-date=21 October 2021}}