SpaceX Falcon 9 Block 5 - Telstar 18 Vantage - Launching September 9, 2018
Screenshot from Tim Dodd hosting SpaceX Falcon 9 launch of Telstar 18 Vantage
Mission Rundown: SpaceX - Telstar 18 Vantage
Written: January 12, 2021
Fourth Falcon leaving the nest
SpaceX got commissioned by Telesat to send the Telstar 18 Vantage satellite towards its transfer orbit. SpaceX will be launching the satellite on top of one of their Falcon 9 rockets delivering it to an elliptical Geostationary Transfer Orbit. The rocket is currently at Cape Canaveral Air Force Station at launch pad SLC-40 in Florida.
The booster B1049-1 supporting this mission is on its maiden voyage, and will after launch land 655 km downrange aboard SpaceX’s autonomous spaceport drone ship ‘Of Course I Still Love You‘ which is the blue dot on the hazard map.
The Block 5 booster has retractable legs, but this time they couldn’t relock the release pins, so the legs had to be removed at Port Canaveral before road transportation.
The fairings are not going to be recovered, because there were no parachutes mounted on the fairings. They will crumble and burn up on reentry some 700 km downrange.
The Payload
Telstar 18V - Telstar 18 Vantage / APStar 5C is a communication satellite in the Telstar series of the Canadian satellite communications company Telesat. T18V will be equipped with C and Ku-band transponders and operate from 138° East. At 7 060 kilograms (15 560 lb), it is the second-heaviest communication satellite ever launched, weighing slightly less than its sibling Telstar 19V.
Telesat signed a contract with SSL in December 2015 for the construction of the satellite. It will be based on the SSL-1300 bus with an electrical output of approximately 14 kW.
The new satellite called Telstar 18 VANTAGE will operate from 138° East and significantly expand Telesat’s capacity over the Asia Pacific region through a combination of broad regional beams and high throughput spot-beams. Telesat also announced it has entered into an agreement with APT Satellite Company Limited (APSTAR) under which APSTAR will make use of capacity on Telstar-18-VANTAGE to serve its growing base of customers. This agreement extends the long term relationship between APSTAR and Telesat that has existed for more than a decade.
Equipped with C and Ku-band transponders, Telstar 18 VANTAGE will offer superior performance for broadcasters, telecom service providers and enterprise networks on the ground, in the air and at sea. Its broad C-band coverage will extend across the Asia region to Hawaii enabling direct connectivity between any point in Asia and the Americas. Its Ku-band capacity will expand on Telesat’s coverage of growing satellite service markets in China, Mongolia, Southeast Asia, and the Pacific Ocean.
Chilling LOX, that’s a great question
FC Guy asks this at 53:53 - How do they chill the densified liquid fuel/oxygen?
At a pressure of 1 bar, the temperature of liquid boiling oxygen stabilizes at 90 Kelvin. For sub-cooling of LOX, the temperature should be lower. It is possible to cool LOX by forced evaporation by a pressure lower than 1 bar. But the LOX tank in a rocket should be as light as possible. If the pressure inside the tank is substantially lower than outside, extra strength and weight is necessary. But according to these papers: (1) (2) and (3) there is another method.
Cold helium gas is injected at the bottom of the tank and the bubbles rise in the LOX. At the surface of the bubbles, LOX evaporates into the bubble and cools the remaining LOX. But extra space is needed for the bubbles in the LOX and for the gas mixture of helium and oxygen above the liquid level. For topping off, the injection of helium is stopped and the remaining space is filled with LOX. Figure 8 of the first paper shows the effect of different helium gas temperatures. The cooling works best with helium at 85 Kelvin, but even helium at 150 Kelvin cools the LOX.
A bubble injected into the LOX consists of 100 % helium and 0 % oxygen at first. The LOX around this bubble would boil just like in a vacuum because the partial pressure of oxygen in this bubble is zero. Even a bubble consisting of 50 % helium and 50 % oxygen is able to cool LOX at 90 K. Without sub cooling in a tank with boiling LOX at 90 K, the gas above the liquid is 100 % oxygen and the partial pressure of oxygen is 1 bar. If the partial pressure of oxygen is lower than 1 bar in the gas above the liquid or inside the bubbles, the LOX is cooled by evaporation.
At the launch pad the LOX may be precooled using a heat exchanger with ground supplied Liquid Nitrogen boiling at 77.355 Kelvin. To save weight of the rocket, this heat exchanger should be outside the rocket but close to it. On photos/videos taken on the pad or launch complex a large liquid Nitrogen tank is seen with a block of long thin Helium tanks which indicates the super chilling heat exchanger.
Liquid Oxygen is pumped to that heat exchanger, where it is super chilled. Liquid Nitrogen and Oxygen should not be mixed to avoid dissolving Nitrogen within the LOX. Cooling with Helium bubbles may be used within the rocket LOX tanks, and the rocket's propellant tanks are being backfilled, pressurized with heated Helium gas for stability during launch.
During LOX loading there is seen venting from the LOX pipes during prefilling, they are not cold enough, the same goes for the rocket LOX tanks, more venting follows and now a running venting of the rocket LOX tanks through the top valves and all of the Merlin rocket engines. Two of which are seen on the black interstage.
The humid ambient air outside the rocket LOX tank gets chilled to form clouds that drift away in the wind depending on the current wind speed. There is an ice build up on the outside of the rocket LOX tanks on the leeward side, and no ice build up where the air gets freeze dried by the freezing cold rocket LOX tanks.
When the rocket LOX tanks get pressurized before launch, ice is seen popping off and you can get an idea about the ice thickness during the LOX loading. Saturn V and the Shuttle main propellant tank both got to accumulate large amounts of frozen ice that would fall off in huge chunks during launching. A fascinating site on the Apollo launches, but a deadly flaw on the Shuttles main propellant tank when frozen chunks of insulation fell off.
Answer given by Uwe on StackExchange, other comments below.
This helium bubbling trick was also used in the shuttle system prelaunch to make sure that the LOX in the long downcomer line stayed nice and cool. Also the Apollo LOX lines in all the stages used Helium bubbles to prevent clogging of LOX pipes preventing them from freezing shut.
@Hobbes Quite late to the party but Helium bubbling was confirmed by Musk in 2016: "Launch aborted on low thrust alarm. Rising oxygen temps due to hold for boat (in the exclusion zone) and helium bubbles triggered alarm." (via twitter) – Christoph Nov 15 '19 at 10:42
