60 years ago: Project Mercury tries for orbit

Sept. 13, 1961: Atlas away!



It’s time.  Time for the Atlas booster to prove itself — or Project Mercury will fall into a world of trouble.  It’s September 13, 1961, launch day for Mercury-Atlas 4 (MA-4), which will attempt to do what MA-3 failed to do on April 25:   Place, an unmanned Mercury capsule in orbit for the first time.  Just a single orbit is planned.  That’s all we need as a starter.

But everything depends on that Atlas, and that booster is not one to depend on.  Developed as the first U.S. intercontinental ballistic missile, first flown in 1957, it’s record is plain dismal.  In 1959, it scored 12 full successes, seven total failures and three partial successes.  In 1960, it achieved 19 successes against fourteen failures and one partial.  

And five months ago, 40 sec. after launch, it failed MA-3.  At just 15,000 ft, the Atlas did not roll onto the proper heading had to be destroyed by range safety.  The booster’s programmer had malfunctioned.

At least the Mercury escape system worked, the tower pulling the capsule free for a safe landing.  Indeed, the same capsule, #8, was in such good condition it was refurbished and sits upon Atlas D #88 today.  

Quality control — that’s a problem.  Indeed, this launch was scheduled for August 26, but just the day before, a lot of defective circuit boards, contaminated with specks of solder, was uncovered.  The boards were used in both the Atlas the the Mercury capsule and had to be replaced. 

All looks “go” for launch on the 13th, at least weather-wise.  Just scattered clouds, visibility 9 mi.   The launch team encounters a couple minor hold, such as to replace a broken screw on the capsule’s shingle-like skin.   At 9 a.m. EDT, T – zero looms.

No doubt about it — this flight it crucial for Mercury and the Atlas.  Critics wonder if the Atlas shouldn’t be replaced by the newer Titan booster, despite the delays that would entail.

If it achieves orbit, MA-4 will an all-up test of the Mercury tracking network of world-spanning stations, completed earlier in the year.  The network will feed data to Mercury Control at Cape Canaveral.  Their names soon would become nearly as familiar as those of the astronauts.  Moving eastward, they were located at:  Grand Bahama Island, Grand Turk Island, Bermuda, Grand Canary Island, a mid-Atlantic tracking ship, Kano (Nigeria), Zanzibar, an Indian Ocean tracking ship, Muchea and Woomera in Australia, the mid-Pacific Island of Canton, Kauai Island (Hawaii), Point Arguello (California), Guaymas (Mexico), White Sands (New Mexico), Corpus Christi (Texas) and Elgin (Florida).

We astronauts are participating around the world for this flight, as we will for all flights.  Alan Shepard, John Glenn and Gus Grissom are on hand at the Cape.  Deke Slayton is at Bermuda where he will monitor orbital insertion and landing.  Scott Carpenter is at the Muchea station.  Gordo Cooper is at Point Arguello.  And Wally Schirra, at Guaymas, will monitor retrofire.   

MA-4 marks the second flight of the modified “thick skinned” Atlas, if you count MA-3 in April, which first employed a beefed up structure.  The stainless steel skin of the missile is like a balloon, so thin that tank pressures keep it ridged.  When it isn’t fueled, it has to be pumped with nitrogen or it will collapse.  Earlier failures indicated that due to the weight and dynamics of the Mercury capsule, the upper part of the structure failed.  On the MA-2 suborbital test, a quick-fix was used — an 8-in. “belly band” below the spacecraft adapter.  That flight, in February, was a success.

Now we about to test the permanent fix.  

At 10:04 a.m. EDT, the three booster engines ignite.  The Atlas uses a “stage-and-a-half” design.  The engines are in a row, the outer booster engines fire for for the first couple minutes, then are, along with the skirt holding them, are jettisoned.  The center sustainer engine continues to fire until orbit is achieved after a flight of about five minutes.

She’s away, but telemetry to Mercury control shows severe vibrations.  Twenty seconds into the flight — the shaking smooths out, and in the next milestone, the vehicle hits “Max Q” the maximum air pressure on it — the zone where MA-1 in 1960 failed.  We pass through it — still go.  At 52 sec. into the flight, an inverter, converting DC to AC power in the capsule’s environmental system fails.  Controllers switch to a backup — and it functions perfectly.

BECO — Booster Engine Cutoff, 2.5 min. after launch.   Altitude 41 mi.  And everything remains go.  The red escape tower above the capsule is jettisoned.

And here it comes — Mercury’s first orbital insertion.  At 4 min. 56 sec. into the flight, SECO — Sustainer Engine Cutoff.  Altitude, 100 mi.; speed 17,400 mph.  Radars feed data to the Goddard Spaceflight Center in Greenbelt, Maryland.  There, IBM 7090 computers calculate the orbit — and determine a go for at least seven orbits.  That doesn’t mean the flight will last that long, only that we now know the orbit itself is stable for at least that long.  (On John Glenn’s flight the same call will create confusion with some who then think the flight is intended to last that long, instead of the planned three orbits.  The mistaken idea that Glenn’s flight was cut short will echo through history.)

The spacecraft achieves an orbit close to predicted — with a low point (perigee) of 99.245 mi., instead of the planned 100.05 mi., and a high point (apogee) of 158.6 mi rather than the planned 154.1 mi.

The troubled Atlas has done its job.  Three small posigrade rockets in the capsule’s retropack fire to push capsule #8 from the booster.  After a 5-sec. pause for vibrations to dampen out, the capsule under autopilot begins turnaround — flipping so the heatshield is in the direction of travel.  The capsule sways in all three directions, yaw, pitch, and roll.  Yet the thrusters overcome it, taking 50 sec. to reach orbital attitude rather than the planned 20 sec., and at the price of 9.5 lbs. of hydrogen peroxide fuel rather than the planned 2.2 lbs.  The trouble later will be traced to a electrical fault in the pitch-rate gyro.

Aboard the capsule, an “astronaut simulator” box consumes oxygen and gives off carbon dioxide like a human.  An array of sensors measures radiation, vibration, noise.   Mercury Control quickly notes high oxygen use.  It was going down fast — due to a valve that snapped open during the launch vibrations.  Before the orbit was over, the primary supply will be depleted, and the system switched to the backup supply.  Such a problem would have been spotted and corrected by an astronaut onboard.

Horizon sensors and attitude gyros maintain the proper orbital orientation, with the nose canted down 34 degrees.  Three times the attitude strays — including just before retrofire — due to the failure of yaw thruster and a roll thruster.  Other thrusters are able to compensate.

Communications carrying both telemetry data and a recorded human voice between the capsule and ground stations prove excellent.  The network passes its first worldwide checkout.

Over the Hawaii area, precisely at 1 hr. 28 min. 59 sec., the automatic timer fires the three solid-fueled retrorockets.  The Guaymus station confirms retrofire, as planned.

The reentry put the heatshield to the test — it needs to withstand a heat pulse with a maximum temperature in excess of 2,000 degrees (F) for eight times times the duration of previous suborbital tests.  The heating, lasting more than 6 min., begins 55 mi. above the earth as the capsule flies 345 mi. east of of Savannah, Georgia.  Maximum heating hits at an altitude of 37 mi., the capsule still moving at about 15,000 mph.  Atmospheric friction quickly slows it.  By the time it reached 12 mi. altitude — in barely more than 3 min. — it is down to 1,350 mph.

At 42,000 ft., the small drogue parachute deploys and stabilizes the capsule, and at 10,000 ft. the 63-ft.-diameter main chute deploys.   And 109 min. after launch, Capsule #8 splashes down 161 mi. east of Bermuda.  It’s condition is excellent.  The flight is an unqualified success.

Project Mercury had done it — achieved orbit.  And the Atlas had done it.  NASA hopes to launch Atlases at 6-8 week intervals.  MA-5, carrying a chimpanzee on a three-orbit flight, could take place in late October.  If that goes smoothly, MA-6, carrying an astronaut could reach orbit in mid-December — the U.S. achieving manned orbital flight before the year of Yuri Gagarin is over.

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