SpaceX Launches NEXT 10 Iridium Satellites For a Fifth Time

Iridium-5 Launch 4
The Falcon 9 F9-52 launching with the Iridium NEXT-5 satellites aboard. Image from SpaceX Flickr.

At 14:13 UTC on March 30th 2018, SpaceX launched a Falcon 9 from foggy Vandenberg Air Force Base. Although designated F9-52 this was the 51st Falcon 9 launch. Using a v1.2 variant booster, the rocket delivered 10 Iridium NEXT satellites into orbit. This was the fifth of eight planned Iridium NEXT missions.

Iridium-5 Launch 2
The Falcon 9 lifting off from Vandenberg AFB california. After the fog had lifted. Image from SpaceX Flickr.

 

From Vandenberg AFB Space Launch Complex 4 East, the first stage of the rocket lasted 2 minutes 34 seconds, separating a few seconds after. The second engine fired for 6 minutes 23 seconds. This part of the webcast was purposefully cut short due to a NOAA remote sensing licensing requirements. This is an issue with SpaceX not having the right licence to broadcast images from certain parts of space. This burn placed the rocket in a roughly 180 x 625 km parking orbit. The Thales Alenia Space satellite then deployed an hour after launch, after a second brief 11 second burn. This put the satellites into a 625km x 86.6 deg orbit.

Iridium-5 Long Exposure
A 53 second long exposure of Falcon 9 F9-52 launching from Vandenberg AFB. Image from SpaceX Flickr.

The rocket used another “Fairing 2.0”, which is slightly larger than usual, but equipped with recovery systems. These systems include thrusters, a guidance system, and a parafoil. The ship, named Mr Steven has a large net to capture the halves of the fairing. Again, the ship failed to catch one of the fairings, due to a parachute system issue. In a tweet by Elon Musk, it was reported that the GPS guided parafoil twisted so the fairing impacted the water at high speed. He also said that SpaceX are doing helicopter drop tests to fix the issue.

Iridium-5 launch 3
The Falcon 9 launching, with a view of the surrounding buildings and fuel tanks. Image from SpaceX Flickr.

Five of the six previously used Falcon 9 vehicles have been fully expended, this was the tenth flight of a previously-flown Falcon 9 first stage. Four of these ten have been purposely expended during their second flight. The first stage (B1041.2) was previously flown during the Iridium NEXT 3 launch on October 9th, 2017. It performed the 2 minute 34 second boost, and performed what SpaceX call a “simulated landing” into the ocean. SpaceX appear to be only launching a reused stages for one reflight, with the soon to launch “block 5” likely to be reused multiple times. Currently the company only have 4 first stages that might be flown, with one allocated for the upcoming CRS-14 dragon resupply mission.

Iridium-5 mission 1
The Falcon 9 F9-52 launching with the Iridium NEXT-5 satellites aboard. Image from SpaceX Flickr.

Explorer 1 and the Van Allen Story

On February 1st, 1958 at 03:48 UTC (January 31st at 22:48 EST), the first Juno booster launched Explorer 1 into Low Earth Orbit. It was the first satellite to be successfully launched by the United States, and the third ever, after Sputnik 1 and 2 in 1957. Launched from the Army Ballistic Missile Agency’s (ABMA) Cape Canaveral Missile Annex in Florida, now known as Launch Complex 26. The launch played a pivotal part in the discovery of the Van Allen Belt, Explorer 1 was the start of the Explorer series, a set of over 80 scientific satellites. Although sometimes looked over in the history of space, it guided the US space program to what it eventually became.

William Hayward Pickering, James Van Allen, and Wernher von Braun display a full-scale model of Explorer 1 at a crowded news conference in Washington, DC after confirmation the satellite was in orbit.

In 1954 The US Navy and US Army had a joint project known as Project Orbiter, aiming to get a satellite into orbit during 1957. It was going to be launched on a Redstone missile, but the Eisenhower administration rejected the idea in 1955 in favour of the Navy’s project Vanguard. Vanguard was an attempt to use a more civilian styled booster, rather than repurposed missiles. It failed fairly spectacularly in 1957 when the Vanguard TV3 exploded on the launchpad on live TV, less than a month after the launch of Sputnik 2. This deepened American public dismay at the space race. Leading to the army getting a shot at being the first american object in space.

The launch
Launch of Jupiter-C/Explorer 1 at Cape Canaveral, Florida on January 31, 1958.

In somewhat of a mad dash to get Explorer 1 ready, the Army Ballistic Missile Agency had been creating reentry vehicles for ballistic missiles, but kept up hope of getting something into orbit. At the same time Physicist James Van Allen of Iowa State University, was making the primary scientific instrument payload for the mission. As well this, JPL director William H. Pickering was providing the satellite itself. Along with Wernher Von Braun, who had the skills to create the launch system. After the Vanguard failure, the JPL-ABMA group was given permission to use a Jupiter-C reentry test vehicle (renamed Juno) and adapt it to launch the satellite. The Jupiter IRBM reentry nose cone had already been flight tested, speeding up the process. It took the team a total of 84 days to modify the rocket and build Explorer 1.

Preparing the explorer 1
Explorer 1 is mated to its booster at LC-26

The satellite itself, designed and built by graduate students at California Institute of Technology’s JPL under the direction of William H. Pickering was the second satellite to carry a mission payload (Sputnik 2 being the first). Shaped much like a rocket itself, it only weighed 13.37kg (30.8lb) of which 8.3kg (18.3lb) was the instrumentation. The instrumentation sat at the front of the satellite, with the rear being a small rocket motor acting as the fourth stage, this section didn’t detach. The data was transmitted to the ground by two antennas of differing types. A 60 milliwatt transmitter fed dipole antenna with two fiberglass slot antennas in the body of the satellite, operating at 108.3MHz, and four flexible whips acting as a turnstile antenna, fed by a 10 milliwatt transmitter operating at 108.00MHz.

Explorer 1 parts
A diagram showing some of the main parts of the Explorer 1 satellite

As there was a limited time frame, with limited space available, and a requirement for low weight, the instrumentation was designed to be simple, and highly reliable. An Iowa Cosmic Ray instrument was used. It used germanium and silicon transistors in the electronics. 29 transistors were used in the Explorer 1 payload instrumentation, with others being used in the Army’s micrometeorite amplifier.  The power was provided by mercury chemical batteries, what weighed roughly 40% of the total payload weight. The outside of the instrumentation section was sandblasted stainless steel  with white and black stripes. There were many potential colour schemes, which is why there are articles models and photographs showing different configurations. The final scheme was decided by studies of shadow-sunlight intervals based on firing time, trajectory, orbit and inclination. The stripes are often also seen on many of the early Wernher Von Braun Rockets.

NASM flight spare
The flight ready spare of the Explorer 1, now shown at the National Air and Space Museum.

The instrument was meant to have a tape recorder on board, but was not modeled in time to be put onto the spacecraft. This meant that all the data received was real-time and from the on board antennas. Plus as there were no downrange tracking stations, they could only pick up signals while the satellite was over them. This meant that they could not get a recording from the entire earth. It also meant that when the rocket went up, and dipped over the horizon, they had no idea whether it got into orbit. Half an hour after the launch Albert Hibbs, Explorers System designer from JPL, who was responsible for orbit calculations walked into the room and declared there was a 95% chance the satellite was in orbit. In response, the Major snapped: “Don’t give me any of this probability crap, Hibbs. Is the thing up there or not?”.

Explorer 1 Mission Badge
The official JPL mission pac=tch for the Explorer 1 mission.

The instrument was the baby of one of Van Allens graduate students, George Ludwig. When he heard the payload was going into the Explorer 1 (and not the Vanguard) he packed up his family and set off for JPL to work with the engineers there. He has a good oral history section on this link, talking about designing some of the first electronics in space. He was there watching the rocket launch and waiting for results. From the Navy’s Vanguard Microlock receiving station they watched the telemetry that reported the health of the cosmic-ray package. The first 300 seconds were very hopeful, with a quick rise in counting rates followed by a drop to a constant 10-20  counts per second, as expected. The calculations told them when they should hear from the satellite again, but 12 minutes after the expected time, nothing showed up but eventually, after pure silence, Explorer 1 finally reported home.

The Van Allen Belt
This diagram showcases the Van Allen belts, which were first detected by instruments aboard Explorer 1 and Explorer 3. The Van Allen belts were the first major scientific discovery of the space age.

Once in orbit, Explorer 1 transmitted data for 105 days. The satellite was reported to be successful in its first month of operation. From the scientist point of view, the lack of data meant the results were difficult to conclude. The data was also different to the expectations, it was recording less meteoric dust than expected and varying amounts of cosmic radiation, and sometimes silent above 600 miles. This was figured out on Explorer 3 when they realised the counters were being saturated by too much radiation. Leading to the discovery of the Van Allen Radiation Belt. Although they described the belt as “death lurking 70 miles up” it actually deflects high energy particles away from earth, meaning life can be sustained on earth. The satellite batteries powered the high-powered transmitter for 31 days, and after 105 days it sent it’s last transmission on May 23rd 1958. It still remained in orbit for 12 years, reentering the atmosphere over the pacific ocean on March 31st after 58,000 orbits.