January 31

31 January 1862

Alvan Graham Clark. Credit: Thomas Rice Burnham

On January 31, 1862, American telescope-maker and astronomer Alvan Graham Clark (1832–1897) made the first observation of Sirius B while testing a new 18.5-inch (470 mm) aperture refractor telescope. Sirius B is the nearest known white dwarf, at 8.6 light years from the Sun. Its existence was deduced in 1844 by German astronomer Friedrich Wilhelm Bessel (1784–1846), from changes in the proper motion of Sirius.

Sirius B has a mass of 1.02 M_☉ (102% of the Sun's), and a diameter of 12,000 km – nearly that of the Earth. It's surface temperature is 25,200 K. The star is primarily composed of a carbon–oxygen mixture that was generated by helium fusion in the progenitor star. This is overlaid by an envelope of lighter elements, with the materials segregated by mass because of the high surface gravity. The outer atmosphere of Sirius B is now almost pure hydrogen and no other elements are seen in its spectrum.

Hubble Space Telescope image of Sirius A and Sirius B. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects. Credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester)

Artist's impression of Sirius A and B. The large, bluish-white star Sirius A dominates the scene, while Sirius B is the small but very hot and blue white-dwarf star on the right. Credit: NASA, ESA and G. Bacon (STScI)

© 2026, Andrew Mirecki

31 January 1961

A three-year-old chimpanzee, named Ham, in the biopack couch for the MR-2 suborbital test flight. Credit: NASA

Mercury-Redstone 2 (MR-2) was launched on a suborbital flight at 16:55 UTC on January 31, 1961, from LC-5 at Cape Canaveral, Florida. The mission was to test the Mercury capsule and the launch vehicle before launching the first American astronaut. The capsule carried a chimpanzee named Ham, the first hominid in space. The capsule and Ham landed safely in the Atlantic Ocean 16 minutes and 39 seconds after launch.

   Officially, Ham was known as “Number 65” before his flight, and only renamed "Ham", after the Holoman Aerospace Medical Center, upon his successful return to Earth. He was taught to pull levers in response to the flashing light. Ham was born in July 1957 and was 3 years 8 months old at launch.

 The objectives of MR-2 were to: (1) obtain physiological and performance data on a primate in ballistic space flight; (2) qualify the Environmental Control System (ECS) and aeromedical instrumentation; (3) qualify the landing bag system; (4) partially qualify the voice communication system; (5) qualify the mechanically actuated side hatch; and, (6) obtain a closed-loop evaluation of the booster automatic abort system.

Chimpanzee Ham is fitted into his special capsule prior to flight on January 31, 1961. He did not wear the helmet on the flight. Credit: NASA/Smithsonian National Air and Space Museum, Herbert Stephen Desind Collection, NASM 9A08100

   During the flight, the thrust controller ran above nominal performance, depleting the propellant 0.5 s before deactivation of the abort pressure sensor. The abort system detected the early shutdown and aborted the spacecraft. The higher-than-normal cut-off velocity coupled with the thrust of the escape engine resulted in the capsule landing well beyond the recovery area. The abort properly signalled the requisite Mayday message to the recovery forces, putting them in motion for a computed rendezvous point further downrange.

   Because of the overperformance of the launch vehicle and the added velocity of the escape engine, MR-2 achieved a velocity of about 9,400 km/hour (as opposed to the intended 7,000 km/hour) and an altitude of 250 km (rather than 185 km). Ham's trip took 2 minutes and 24 seconds longer than intended (16 minutes and 39 seconds total flight time) and went 670 km downrange (205 km further than planned). His peak g-load during reentry was 14.7, almost 3g more than planned.

Mercury-Redstone 2 launch with chimpanzee Ham aboard. Credit: NASA

   Problems also occurred with regard to the cabin pressure when, just prior to the abort, at 2 minutes and 18 seconds into the flight, it dropped from 5.5 psi to 1 psi. The problem was ultimately traced to the air inlet snorkel valve. Vibrations had loosened the pin which held the valve closed, thus allowing the valve to open, an event which was normal only after the main parachute was deployed. Ham, inside his space suit, did not suffer from this sudden depressurization of the cabin. However, the open valve contributed to problems after splashdown. Ham's performance during the flight went well, with reaction times for his required tasks of lever pulling comparable to his pre-flight testing despite his vehicle's performance problems.

   When MR-2 splashed down no ships had yet reached the vicinity, having landed some 100 km from the nearest recovery ship, the destroyer USS Ellison. A P2V search plane located the capsule about 27 minutes after splashdown. Helicopters were dispatched from the USS Donner as at least two additional hours were still required for the Ellison to arrive. Although when the search plane had located the capsule it was floating upright, by the time the helicopters arrived they found MR-2 on its side and taking on water. It was determined that the beryllium heatshield had skipped on the water on impact, bouncing against the capsule bottom and puncturing two holes in the titanium pressure bulkhead. In addition, the plastic landing bag had worn badly, resulting in the heat shield being torn free. Water entering the cabin became worse when the capsule capsized, allowing more water to enter via the open cabin pressure valve. When the helicopter latched onto the capsule, the pilot estimated an extra load of nearly 800 pounds due to the sea water. Ham was returned safely to the USS Donner, apparently no worse for the wear.

The famous "handshake" welcome. After his flight, the seemingly unfazed chimpanzee Ham is greeted by the commander of the recovery ship, USS Donner. Credit: NASA, color correction by Andrzej Mirecki

© 2026, Andrew Mirecki

31 January 1966

Model of a Ye-6 series lunar spacecraft

On January 31, 1966, at 11:41:37 UTC, Luna 9 (Ye-6 No.13), the first spacecraft to achieve a survivable landing on the Moon, was launched from Baikonur. It landed in Oceanus Procellarum on February 3, 1966.

Model of Luna 9 lander. Credit: Roscosmos

Full Description from NASA Space Science Data Coordinated Archive:

Spacecraft and Subsystems 

   The spacecraft comprised two parts, which had a total mass of 1,538 kg and stood 2.7 meters tall. The Luna 9 automatic lunar station that achieved the soft landing was a spherical body with a diameter of 58 centimeters and a mass of 99 kg. The station consisted of a hermetically sealed container, pressurized to 1.2 atmospheres, which held the radio system, programming device, batteries, thermal control system and scientific apparatus. Four antennas that automatically opened after landing were mounted on the outside of the compartment. An airbag amortization system to cushion the landing was also mounted outside the station.

   The entire compartment was mounted above a flight stage which held the main KTDU-5A retrorocket, four outrigger vernier rockets, a toroidal aluminum alloy fuel tank, a 90 cm diameter spherical oxidizer tank, fuel pumping system, the nitrogen tank for airbag inflation, and guidance and landing sensor equipment. This equipment included gyroscopes, electro-optical apparatus, the soft-landing radar system, and small orientation engines. Compartments on either side of the main body with a total mass of 300 kg contained guidance radar and the 3 nitrogen jets and gas bottles of the attitude control system for the cruise stage, designed to be jettisoned once the descent was underway. The total propellant load (amine-based fuel and nitric acid oxidizer) was about 800 kg.

   The scientific equipment comprised a lightweight (1.5 kg) panoramic television camera and an SBM-10 radiation detector. A mirror on an 8 cm turret was mounted on the top of the lander above the camera to allow 360 degree coverage. The scientific container was designed to separate from the flight stage immediately before touchdown. The thermal control system maintained the interior temperature between 19 and 30 degrees C. All operations were battery powered.

Mission Profile

   The Luna 9 payload was carried to Earth orbit by an A-2-E vehicle and then conveyed toward the Moon by a fourth stage rocket that separated itself from the payload on January 31. The spacecraft spun up to 0.67 rpm by the nitrogen jets. A mid-course correction, involving a 48 second burn, took place on 1 February at 19:29 UT (22:29 Moscow time), resulting in a delta-V of 71.2 m/sec.

   At an altitude of 8300 km the spacecraft was oriented for retro-rocket firing and its spin was stopped. At 75 km altitude, 48 seconds before landing at a velocity of 2.6 km/s, the radar altimeter sent commands to jettison the side modules, inflate the airbags, and begin retrorocket firing. At 250 meters from the surface the main retrorocket was turned off and the four outrigger engines were used to slow the craft. At a height of about 5 meters a contact sensor touched the ground, the engines were shut down, and the landing capsule was ejected, impacting the surface at 22 km/hr, bouncing several times and coming to rest in Oceanus Procellarum (Ocean of Storms) west of Reiner and Marius craters at approximately 7.08 N, 64.37 W on February 3, 1966 at 18:45:30 UT (21:45:30 Moscow time).

   After about 250 seconds the four petals, forming the top shell of the spacecraft, opened outward and stabilized the spacecraft on the lunar surface. Spring-controlled antennas assumed operating positions, and the television camera rotatable mirror system, which operated by revolving and tilting, began a photographic survey of the lunar environment 250 seconds after landing. The first test image, which showed very poor contrast because the Sun was only about 3 degrees above the horizon, was completed 15 minutes later. Seven radio sessions, totaling 8 hours and 5 minutes, were transmitted as were three series of TV pictures. When assembled, the photographs provided four panoramic views of the nearby lunar surface.

   The pictures included views of nearby rocks and of the horizon 1.4 km away from the spacecraft. They showed Luna 9 had landed near the rim of a 25 meter diameter crater at a tilt of about 15 degrees. The probe took the first full panorama on 4 February from 1:50 to 3:30 UT, with the Sun 7 degrees above the horizon. After the first panorama was taken the probe slipped as the regolith on the slope settled, and was at a 22.5 degree tilt when the second panorama was taken at 15:30 to 17:10 UT on 4 February. Two more panoramas were obtained, on 5 February from 16:00 to 17:40 UT, and the next day from about 20:00 to 21:00 UT. The pictures included views of nearby rocks and of the horizon 1.4 km away from the spacecraft. Radiation data were also returned, showing a dosage of about 30 millirads per day. On 6 February at 22:55 UT the batteries ran out of power and the mission ended.

© 2026, Andrew Mirecki