Explorer 24

{{Infobox spaceflight

| name = Explorer 24

| names_list = AD-B
Air Density experiment-B

| image = Explorer 24.jpg

| image_caption = Explorer 24 satellite

| image_size = 300px

| mission_type = Air density

| operator = NASA

| COSPAR_ID = 1964-076A

| SATCAT = 00931

| mission_duration = 1426 days (achieved) {{cite web|url=https://www.lib.cas.cz/space.40/1964/076A.HTM|title=Explorer 24 - 1964-076A|publisher=Lubor Lejček, Antonín Vítek|language=cs|access-date=10 June 2018}}

| spacecraft = Explorer XXIV

| spacecraft_type = Explorer

| spacecraft_bus = AD

| manufacturer = Langley Research Center

| launch_mass = {{cvt|8.6|kg}}

| dimensions = {{cvt|3.6|m}} diameter

| power = Solar cells and
rechargeable batteries

| launch_date = 21 November 1964, 17:09:39 GMT{{cite web|url=http://www.planet4589.org/space/log/launchlog.txt/|publisher=Jonathan's Space Report|title=Launch Log|access-date=June 10, 2018|archive-date=14 November 2021|archive-url=https://web.archive.org/web/20211114093153/https://planet4589.org/space/log/launchlog.txt|url-status=dead}}{{cite web|url=http://www.unoosa.org/documents/pdf/inf088E.pdf/|title=Letter dated 5 February 1965 from the Permanent Representative of the United States of America addressed to the Secretary-General|work=COMMITTEE ON THE PEACEFUL USES OF OUTER SPACE|publisher=UNOOSA|date=November 30, 1964|access-date=10 June 2018|archive-url=https://web.archive.org/web/20180505205224/http://www.unoosa.org/documents/pdf/inf088E.pdf|archive-date=5 May 2018|url-status=dead}}

| launch_rocket = Scout X-4 (S-135R) {{cite encyclopedia|title=Explorer|url=http://www.astronautix.com/e/explorer.html/|archive-url=https://web.archive.org/web/20161227205032/http://astronautix.com/e/explorer.html|url-status=dead|archive-date=27 December 2016|publisher=Encyclopedia Astronautica |access-date=10 June 2018}}

| launch_site = Vandenberg, PALC-D

| launch_contractor = Vought

| entered_service = 21 November 1964

| last_contact =

| destroyed =

| decay_date = 18 October 1968

| orbit_reference = Geocentric orbit{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1964-076A|title=Trajectory: Explorer-24 (S-55C) 1964-076A |publisher=NASA|date=28 October 2021|access-date=7 November 2021}} {{PD-notice}}

| orbit_regime = Low Earth orbit

| orbit_periapsis = {{cvt|525|km}}

| orbit_apoapsis = {{cvt|2498|km}}

| orbit_inclination = 81.40°

| orbit_period = 116.30 minutes

| apsis = gee

| instruments = Nonsystematic Changes of Air Density
Systematic Changes of Air Density

| programme = Explorer program

| previous_mission = Explorer 23

| next_mission = Explorer 25

}}

Explorer 24 (also called AD-B, Air Density experiment-B and S-56C) was a NASA satellite designed for atmospheric studies. Explorer 24 was launched on 21 November 1964 from Vandenberg Air Force Base, Lompoc, California, with a Scout X-4. Explorer 24 was launched along with its successor satellite, Explorer 25.{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1964-076A|title=Dispaly: Explorer-24 (S-55C) 1964-076A|publisher=NASA|date=28 October 2021|access-date=7 November 2021}} {{PD-notice}}

Spacecraft

Explorer 24 was placed in orbit together with Explorer 25 from a single launch vehicle. Explorer 24 was identical in configuration to the previously launched balloon satellites Explorer 9 and Explorer 19. The spacecraft was {{cvt|3.6|m}} in diameter, was built of alternating layers of aluminum foil and plastic film, and was covered uniformly with {{cvt|5.1|cm}} white dots for thermal control. It was designed to yield atmospheric density near perigee as a function of space and time from sequential observations of the sphere's position in orbit. To facilitate ground tracking, the satellite carried a 136-MHz tracking beacon.

Experiments

= Nonsystematic Changes of Air Density =

This experiment was designed to determine nonsystematic changes of the density of the upper atmosphere from studies of the drag on a {{cvt|3.6|m}} diameter low-density sphere caused by short-term differences in solar activity. Density values near perigee were deduced from sequential observations of the spacecraft position, using optical (Baker-Nunn camera network) and radio and/or radar tracking techniques. This experiment resulted in the successful determination of reasonable density values until spacecraft re-entry.{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1964-076A-01|title=Experiment: Nonsystematic Changes of Air Density|publisher=NASA|date=28 October 2021|access-date=7 November 2021}} {{PD-notice}}

= Systematic Changes of Air Density =

This experiment was designed to determine systematic changes of air density as a function of altitude, latitude, and time of day, by measuring the drag on a {{cvt|3.6|m}} diameter low-density sphere with ground tracking.{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1964-076A-02|title=Experiment: Systematic Changes of Air Density|publisher=NASA|date=28 October 2021 |access-date=8 November 2021}} {{PD-notice}}

Results

Explorer 24 helped determine the variation in density between the day and night of the Earth and gave rise to studies on the zone winds in the exosphere, at an altitude of between {{cvt|450|km}} and {{cvt|620|km}}.{{cite journal|title=The Shape and Location of the Diurnal Bulge in the Upper Atmosphere|journal=SAO Special Report|date=1966|bibcode=1966SAOSR.207.....J|last1=Jacchia|first1=L. G. |last2=Slowey|first2=J.|volume=207}}{{cite journal|title=Exospheric zonal winds between 540 and 620 km from the orbit of Explorer 24|journal=Planetary and Space Science|date=June 24, 1976 |bibcode=1976P&SS...24..529B|last1=Blum|first1=P. W.|last2=Schuchardt|first2=K. G. H.|volume=24|issue=6|page=529|doi=10.1016/0032-0633(76)90131-8}}

The satellite reentered the Earth's atmosphere on 18 October 1968.

References

Category:Spacecraft launched in 1964

Category:Explorers Program

Category:Balloon satellites