A tripropellant rocket is a rocket that uses three propellants, as opposed to the more common bipropellant rocket or monopropellant rocket designs, which use two or one propellants, respectively. Tripropellant systems can be designed to have high specific impulse and have been investigated for single stage to orbit designs. While tripropellant engines have been tested by Rocketdyne and Energomash, no tripropellant rocket has been built or flown. There are two different kinds of tripropellant rockets. One is a rocket engine which mixes three separate streams of propellants, burning all three propellants simultaneously; the other kind of tripropellant rocket is one that uses one oxidizer but two fuels, burning the two fuels in sequence during the flight. Simultaneous tripropellant systems involve the use of a high energy density metal additive, like beryllium or lithium, with existing bipropellant systems. In these motors, the burning of the fuel with the oxidizer provides activation energy needed for a more energetic reaction between the oxidizer and the metal.
While theoretical modeling of these systems suggests an advantage over bipropellant motors, several factors limit their practical implementation, including the difficulty of injecting solid metal into the thrust chamber. In the 1960s, Rocketdyne fired an engine using a mixture of liquid lithium, gaseous hydrogen, liquid fluorine to produce a specific impulse of 542 seconds the highest measured such value for a chemical rocket motor. In sequential tripropellant rockets, the fuel is changed during flight, so the motor can combine the high thrust of a dense fuel like kerosene early in flight with the high specific impulse of a lighter fuel like liquid hydrogen in flight; the result is a single engine providing some of the benefits of staging. For example, injecting a small amount of liquid hydrogen into a kerosene-burning engine can yield significant specific impulse improvements without compromising propellant density; this was demonstrated by the RD-701 achieving a specific impulse of 415 seconds in vacuum, where a pure kerosene engine with a similar expansion ratio would achieve 330–340 seconds.
Although liquid hydrogen delivers the largest specific impulse of the plausible rocket fuels, it requires huge structures to hold it due to its low density. These structures can weigh a lot, offsetting the light weight of the fuel itself to some degree, result in higher drag while in the atmosphere. While kerosene has lower specific impulse, its higher density results in smaller structures, which reduces stage mass, furthermore reduces losses to atmospheric drag. In addition, kerosene-based engines provide higher thrust, important for takeoff, reducing gravity drag. So in general terms there is a "sweet spot" in altitude where one type of fuel becomes more practical than the other. Traditional rocket designs use this sweet spot to their advantage via staging. For instance the Saturn Vs used a lower stage powered by RP-1 and upper stages powered by LH2; some of the early Space Shuttle design efforts used similar designs, with one stage using kerosene into the upper atmosphere, where an LH2 powered upper stage would light and go on from there.
The Shuttle design is somewhat similar, although it used solid rockets for its lower stages. SSTO rockets could carry two sets of engines, but this would mean the spacecraft would be carrying one or the other set "turned off" for most of the flight. With light enough engines this might be reasonable, but an SSTO design requires a high mass fraction and so has razor-thin margins for extra weight. At liftoff the engine burns both fuels changing the mixture over altitude in order to keep the exhaust plume "tuned" switching to LH2 once the kerosene is burned off. At that point the engine is a straight LH2/LOX engine, with an extra fuel pump hanging onto it; the concept was first explored in the US by Robert Salkeld, who published the first study on the concept in Mixed-Mode Propulsion for the Space Shuttle, Astronautics & Aeronautics August 1971. He studied a number of designs using such engines, both ground-based and a number that were air-launched from large jet aircraft, he concluded that tripropellant engines would produce gains of over 100% in payload fraction, reductions of over 65% in propellant volume and better than 20% in dry weight.
A second design series studied the replacement of the Shuttles SRBs with tripropellant based boosters, in which case the engine halved the overall weight of the designs. His last full study was on the Orbital Rocket Airplane which used both tripropellant and a plug nozzle, resulting in a spaceship only larger than a Lockheed SR-71, able to operate from traditional runways. Tripropellant engines were built in Russia. Kosberg and Glushko developed a number of experimental engines in 1988 for a SSTO spaceplane called MAKS, but both the engines and MAKS were cancelled in 1991 due to a lack of funding. Glushko's RD-701 was built and test fired and although there were some problems, Energomash feels that the problems are solvable and that the design does represent one way to reduce launch costs by about 10 times
Staple Island is a small rocky island, or skerry, one of the Outer Group of the Farne Islands in Northumberland, England. The Farne Islands are a designated National Nature Reserve. Staple Island is an important wildlife habitat known for its prolific breeding colonies of Atlantic puffins and kittiwakes. A notable colony of grey seals breeds on the island with pups born every year in September–November; the island has no permanent population but local boats are licensed to land passengers. The National Trust has bird wardens on site during part of the year. Although now uninhabited, the island has a history associated with the early monastic settlement of nearby Lindisfarne. Views to the south range as far as Dunstanburgh Castle and along the north mainland shore to Bamburgh Castle. A lighthouse was built on Staple Island in 1778 and blown down in 1784. Auk Skerry Information on the Farne Islands, North Sunderland and Seahouses. Farne Islands information at the National Trust Farne Islands access and information Northumberland Coast — Area of Outstanding Natural Beauty — Northumberland Coast AONB Site
Susanna Dinnage is a British businesswoman, the current global president of the Animal Planet television network. In November 2018, she became the chief executive-designate of the English Premier League, was scheduled to succeed Richard Scudamore in early 2019. On 30 December 2018, Dinnage told the organisation. Dinnage started her career at MTV Networks, she worked for Channel 5 for more than ten years from its creation in 1997. In 2009, Dinnage joined Discovery, Inc. and ran its British and Irish operation, including responsibility for Eurosport. During her time at Discovery, Eurosport obtained the European coverage rights to all Summer and Winter Olympic Games from 2018-2024. In November 2017, she was appointed the first global president of the Animal Planet network, owned by Discovery, Inc. Dinnage is the chair of the Commercial Broadcasters Association, an executive member of the Discovery Women's Network. In 2017, she was a leading contender to become chief executive of Channel 4, although the position was given to Alex Mahon instead.
In November 2018, Dinnage was chosen to succeed Richard Scudamore as chief executive of the English Premier League. She was the Premier League recruitment panel's preferred candidate, her appointment was voted for by all 20 Premier League teams. Had she taken up the post in early 2019, Dinnage would have become the most senior female leader in major professional sport, the fourth Premier League chief since the formation of the Premier League in 1992, the first female Premier League chief. On 30 December 2018, Dinnage told the organisation. Dinnage lives in London, she is a Fulham season ticket holder