{"id":37281,"date":"2020-12-03T19:23:00","date_gmt":"2020-12-03T11:23:00","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/solid-rocket-stages-and-how-they-perform-mission-precise-orbit-insertions\/"},"modified":"2020-12-03T19:23:00","modified_gmt":"2020-12-03T11:23:00","slug":"solid-rocket-stages-and-how-they-perform-mission-precise-orbit-insertions","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/solid-rocket-stages-and-how-they-perform-mission-precise-orbit-insertions\/","title":{"rendered":"Solid rocket stages and how they perform mission-precise orbit insertions"},"content":{"rendered":"

Most rocket launches culminate with liquid-fueled upper stage engines turning off at exactly the precise millisecond a host of parameters \u2014 such as flight path angle, orbital inclination, apogee, and perigee \u2014 are all met simultaneously.<\/p>\n

So then how do solid propellant upper stages like those used on the Antares, Pegasus, and Minotaur fleets from Northrop Grumman perform those same types of mission-precise orbital insertions when solid propellant stages cannot be turned off once ignited?<\/p>\n

In short, there are three issues that must be addressed.<\/p>\n<\/p>\n

Issue #1: You can\u2019t turn off solid rocket motors<\/b><\/p>\n

\u201cThere are three issues with solids,\u201d said Mike Ruth, Northrop Grumman Fellow, <\/b>in an interview with NASASpaceflight.  \u201cThe first is that you can\u2019t turn them off.  The second one is that they have short and impulsive burns.  And the third is that you need to bleed off extra energy.\u201d<\/p>\n

\u201cSo the first one is: we can\u2019t turn the rocket off.  So what do we do about that?\u201d asked Mike.  \u201cThe basic fix is that we have a very rigorous process for predicting the energy on board the engines.\u201d<\/p>\n

Kurt Eberly, Director Space Launch Programs, Northrop Grumman, added, \u201cThe key to targeting a [solid] vehicle is knowing how much energy we\u2019re going to get out of the stage when the final grain of propellant is burned.  And this starts back at the Solid Rocket Booster manufacturing facility and our propulsion systems business unit in Utah, formerly ATK.\u201d<\/p>\n

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The first step in the process after a solid rocket motor case is wound together to form a composite case is to determine its dry mass by weighing it before any propellant is added.  <\/p>\n

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Technicians (one inside the segment, one outside) inspect the propellant grain of a Solid Rocket Booster segment for the Space Shuttle (Credit: NASA)<\/p>\n

Afterward, the propellant \u2014 a very viscous product at this stage \u2014 is poured into the casing and allowed to cure until hardened.  A small amount, 1 pound, is kept from each batch.  This is called a 1-pound charge and is a very critical part of the data used to design the flight profile for each solid motor upper stage.<\/p>\n

\u201cOf these mixes of propellant, a little bit of it is put to the side, called a 1-pound charge, and then we take that into a test facility, and we burn it, and we measure the energy output from the burn,\u201d said Kurt.<\/p>\n

Here, the precisely calibrated estimate of the total energy of the stage can be determined when combined with a second weighing of the motor case after the propellant is cured and machined to its proper shape.  The difference between the dry mass and fueled mass gives the precise mass of the propellant\u2026 which coupled with the measurement of the burn energy of the 1-pound charge provides the detailed estimate for the total energy in the stage.<\/p>\n

\u201cSo then our propulsion system group puts that all into a ballistics report for us, all these weights and energy that we\u2019re going to get, and so on, and then they send that to us over at Launch Vehicles.  And then we take that ballistics report and we do our own modeling,\u201d added Kurt.<\/p>\n

Mike Ruth then continued, \u201cSo we take that data and a ballistics file \u2014 and that\u2019s basically the main data set for what the predicted or nominal history vs time of the engine thrust vs. the remaining propellant mass.\u201d<\/p>\n

\u201cThat gets incorporated into the simulation, and then maybe an even more important piece of data which is the dispersions we need to assume \u2014 a measure of how confident the vendor is in their prediction of the energy, the exact amount of energy that\u2019s on the stage.  And for solid booster guidance, we make very careful use of the predictions of how much energy we nominally have on board.\u201d<\/p>\n<\/p>\n