Last Updated Dec 20, 2015 4:50 PM EST
Making its first flight since a catastrophic launch failure last June, SpaceX is readying an upgraded Falcon 9 rocket for launch Monday evening to boost 11 small Orbcomm data relay satellites into orbit. In a major space "first," the rocket's first stage will attempt a landing back at the Cape Canaveral launch site to demonstrate reusability, a key requirement for lowering commercial launch costs.
In another first, the Falcon 9 will use colder, denser-than-usual liquid oxygen and kerosene propellants, a significant upgrade allowing the booster's nine Merlin 1D first-stage engines to generate more power, increasing their combined liftoff thrust from 1.3 million pounds to 1.5 million, or 170,000 pounds of thrust per engine.
The new system, including extensive launch pad modifications, was put to the test last week when the rocket was erected at the pad and fueled for an engine test firing. Engineers ran into a variety of glitches that ultimately delayed the "static" firing for two days. But on Friday, the work paid off and the engines were briefly ignited to verify good performance.
SpaceX had planned to launch the rocket Sunday, but company founder Elon Musk ordered a 24-hour delay, to 8:33 p.m. EST (GMT-5) Monday, to improve the odds of a successful first stage landing. The forecast calls for an 80 percent chance of favorable weather.
"Just reviewed mission params w SpaceX team," Musk tweeted. "Monte Carlo (statistical analysis) runs show tmrw night has a 10% higher chance of a good landing. Punting 24 hrs."
Orbcomm reported on its website the delay would allow "an additional day for more analysis and time to further chill the liquid oxygen in preparation for launch."
Increasing the Falcon 9's thrust will allow SpaceX to launch heavier payloads, a key issue in the commercial satellite industry. Perhaps more important over the long haul, Musk believes the only way to dramatically lower launch costs is to recover, refurbish and reuse spent rocket stages.
SpaceX carried out two attempts to land a Falcon 9 first stage on an off-shore barge, demonstrating the booster's ability to autonomously slow down, re-enter the atmosphere and descend to a powered, tail-first landing.
In the first attempt, a hydraulic system failure resulted in a crash landing on the barge. In the second, the booster managed to set down on the barge but tipped over and exploded.
In both cases, the rocket's control software worked properly and left little doubt SpaceX could get a Falcon 9 first stage back to a landing target. But the Air Force, which manages the Florida launch site, had to be convinced a returning booster posed no credible threat to life or property.
Like all rockets launched from the East Coast, the Falcon 9 was equipped with a self-destruct system under the control of Air Force range safety officers.
While no details have been provided, SpaceX was cleared to attempt a touchdown at "Landing Site 1," an abandoned Atlas ICBM launch complex the company leases at the Cape Canaveral Air Force Station. Area residents were warned they might hear a sonic boom during the booster's approach.
Playing it safe, the Air Force was expected to enforce a large buffer zone, clearing personnel from the immediate area in case the returning rocket somehow went awry. News media, which typically cover SpaceX launchings from a causeway about three miles from the pad, were relocated to Port Canaveral some 14 miles from the launch site and about eight miles from the landing zone.
But the landing attempt, however important to SpaceX's long-range plans, is a purely secondary objective. The primary goals of the flight are to test the new rocket and to deploy 11 small Orbcomm satellites, each weighing about 380 pounds, into a 400-mile-high orbit. The satellites are part of a growing constellation of Orbcomm spacecraft that provides data relay services.
The company launched six satellites on a previous SpaceX mission, although one failed after reaching orbit. Overall, Orbcomm operates a constellation of 34 spacecraft.
Orbcomm CEO Marc Eisenberg told Spaceflight Now that his company has enjoyed a good relationship with SpaceX and that he had no qualms being the first customer on the upgraded Falcon 9.
"This is certainly an upgraded rocket," he said. "There's also, if you look at the margins and everything, there's a little bit more redundancy in this rocket as well. I'm feeling pretty good about that. Return-to-flight missions also typically have better success rates than standard missions, but you're also aware that you need your backup plans just in case, and there's a reason to buy insurance."
The upgraded Falcon 9 is five feet taller than the previous version -- 229 feet -- and features an extended "interstage" section separating the first and second stages, along with an improved stage separation system. The second stage propellant tanks were extended and its single Merlin 1D engine features a longer nozzle and can generate 210,000 pounds of thrust in vacuum.
All 10 engines burn refined kerosene fuel, known as RP-1, and liquid oxygen. Liquid oxygen has a temperature of around minus 298 degrees Fahrenheit, but during tests last week Musk tweeted the oxygen on board the upgraded rocket is cooled to minus 340 degrees. The RP-1, which normally is stored at a room temperature 70 degrees, is chilled to 20 degrees.
"The thrust is higher, we've improved the stage separation system, we stretched the upper stage of the rocket to add more propellant to that. There are a number of other improvements in electronics. It's a significantly improved rocket from the last one."
The launching is a critical milestone for SpaceX.
Along with clearing the way for two more launches in January, a successful flight Monday also is expected to help pave the way for SpaceX to resume space station cargo delivery flights in early February under a $1.6 billion contract with NASA to deliver some 44,000 pounds of cargo and supplies over 12 flights.
The company's seventh operational resupply mission ended in a spectacular failure June 28 when a defective strut inside a Falcon 9's second stage liquid oxygen tank broke away, releasing a high-pressure helium tank and triggering a catastrophic in-flight breakup.
After a lengthy failure investigation, SpaceX took action to make sure no defective struts could find their way into downstream rockets. At the same time, engineers pressed ahead with the modifications allowing the rocket to generate additional launch power through the use of densified liquid oxygen.
Given the failure in June, NASA managers told Musk the agency did not want to resume SpaceX resupply flights until after the upgraded rocket had flown at least once. Along with the Orbcomm launch Monday, SpaceX plans to launch an SES communications satellite sometime in January, along with a NASA ocean research satellite on Jan. 17.
The SES launch will use the upgraded Falcon 9 while the NASA research satellite uses the earlier version.
Assuming those flights go well, NASA is targeting Feb. 7 for the next SpaceX station resupply flight.
SpaceX is one of two companies with NASA resupply contracts. Orbital ATK holds a $1.9 billion contract with NASA to deliver some 20 tons of supplies and equipment. Like SpaceX, Orbital suffered a catastrophic launch failure Oct. 28, 2014, when a company-designed Antares rocket exploded seconds after liftoff.
The disaster grounded Orbital for a full year, but the company returned to flight Dec. 3 using a United Launch Alliance Atlas 5 rocket to boost a Cygnus cargo ship to the space station. Another Atlas 5/Cygnus launch is planned for March 10, following by the first flight of a redesigned Antares at the end of May.
While Orbital hopes to sell its Antares for commercial flights down the road, NASA is the rocket's only current customer. SpaceX is relying on its upgraded Falcon 9 to carry a full manifest of NASA, military and civilian satellites into orbit.
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