{"id":41242,"date":"2008-12-09T18:47:25","date_gmt":"2008-12-09T10:47:25","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/ares-i-thrust-oscillation-meetings-conclude-with-encouraging-data-changes\/"},"modified":"2008-12-09T18:47:25","modified_gmt":"2008-12-09T10:47:25","slug":"ares-i-thrust-oscillation-meetings-conclude-with-encouraging-data-changes","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/ares-i-thrust-oscillation-meetings-conclude-with-encouraging-data-changes\/","title":{"rendered":"Ares I Thrust Oscillation meetings conclude with encouraging data, changes"},"content":{"rendered":"

A series of Ares I Thrust Oscillation (TO) meetings have concluded with the decision to recommend baselining Ares I\u2019s Tuned Mass Absorber (TMA) on the aft of the vehicle as a passive \u2013 as opposed to active \u2013 system, as the latest analysis \u2013 which has included human tests \u2013 reduce TO as a potential LOV\/C (Loss of Vehicle and Crew) event to 1 in 150,000. Notes also reference that TO may not even affect Orion on two out of three launches, according to the latest computational data.<\/p>\n

 <\/p>\n

Also known as \u201cResonant Burning\u201d \u2013 described as vortices that shed within the solid rocket motors during combustion due to the shearing of internal flow at propellant discontinuities \u2013 the issue relates to when the frequency of thrust oscillations is coincident with the acoustic modes of the motor cavity.<\/p>\n

When pressure oscillations drive resonant modes in the vehicle structure, these oscillations are capable of rendering the astronauts incapacitated, or worse.<\/p>\n

This was the major concern, that crew health was at risk during the few seconds TO occurs late in first stage flight. However, via recent engineering work that has created several options to mitigate TO on Ares I\u2019s first stage reaching the crew seated in Orion, this risk has \u2013 it\u2019s claimed \u2013 been eliminated.<\/p>\n

This left engineers with the challenge of ensuring the mitigation techniques countered any potential issues of crew function \u2013 in other words, that TO would not hinder the crew from carrying out manual commands during the four to five seconds of a TO event during first stage.<\/p>\n

\"\"Currently two engineering options have been baselined into the vehicle, with a third likely to be added during next year\u2019s Ares I Delta PDR (Preliminary Design Review).<\/p>\n

One is a set of \u201cshock absorbers\u201d that will be added to the aft skirt of Ares I. Known in some documentation as the Skirt TOA (Tuned Oscillating Arrays) Concept, but commonly known as the Tuned Mass Absorbers (TMA) concept, 16 actuators are placed around the circumference of the aft to counter the oscillations.<\/p>\n

SpaceX<\/path>SpaceX launch tickets<\/path>Rocket launch schedules<\/path>\n

(adsbygoogle = window.adsbygoogle || []).push({});<\/p>\n

This was classed as an active system \u2013 one which would react to the oscillations as required, with the contingency of still being able to mitigate a large amount of TO, should one or more actuators failed.<\/p>\n

This has since moved to a passive system, following the series of meetings that concluded last week.<\/p>\n

Some engineers at the Marshall Space Flight Center (MSFC) are still arguing for an active system, with findings heading to NASA HQ this week for review by NASA administrator Mike Griffin, who is continuing to be \u2018hands on\u2019 with Ares I\/Orion\u2019s development.<\/p>\n

The final decision will be important, due to the passive system holding less mass penalties on the vehicle than the active concept, along with an indication into the current level of confidence that TO is losing its footing as a major problem for Ares I.<\/p>\n

The second area of mitigation is at the interstage are of Ares I.<\/p>\n

\"\"This concept is called the SoftRide Isolator \u2013 a set of 200 brackets, weighing a total of two tons, that fit around the circumference of the joint between the frustum and interstage.<\/p>\n

Notes of concern were raised a few months ago, relating to their ability to mitigate the oscillations as planned, and that they could exacerbate potential vehicle buckling at the interstage. This was know as \u201clocal bending moment due to load eccentricity\u201d.<\/p>\n

This led to a redesign of the isolators to \u201creduce or eliminate\u201d that threat. Work is continuing on the design, though it remains baselined as one of the main elements of TO mitigation at this time.<\/p>\n

The third option \u2013 which was deferred until 2009 in order to avoid a delay to August\u2019s main PDR for Ares I \u2013 relates to isolating the crew seats from most of the remaining oscillations that could ride up the vehicle from the first stage.<\/p>\n

This remains on the cards for being added to Orion in 2009, following its references in the latest meetings, which backs up the documentation from Orion\u2019s Lockheed Martin engineers that the isolation \u2018crate\u2019 will become a \u201cChange Request\u201d in 2009 \u2013 which they complained was yet another change to the vehicle, causing problems with their wish to work with a stable design.<\/p>\n

Notes from the meetings (listed on L2) make for interesting reading, with most of the previous engineering overviews showing wide-scale concerns about both the effect of TO on the vehicle, and issues with the planned mitigation techniques. Notes from previous meetings have almost been completely detached from the overly positive overviews given by Ares I managers at media briefings.<\/p>\n

However, the latest meeting shows a sea change towards the positive, following an overview of analysis work that has been carried out over the last few months.<\/p>\n

It is now understood that there is close to an engineering consensus that the combined mass absorbers on the aft, in combination with the interstage isolator are deemed as capable of \u201cdoing the job\u201d.<\/p>\n

That job is to ensure crew health remains within requirements when TO occurs during late first stage flight, and within the limits of crew function. The latest risk number of 1 in 150,000 relates to an incident where the crew have to carry out a manual function in Orion, during the five seconds of a TO event.<\/p>\n

Engineers found that the only time a manual command would be required at this stage of flight would be via the need to manually abort the mission. Given the onboard computers handle such aborts, the manual command would only be required during a severe system failure \u2013 such as an automated failure of Orion\u2019s flight computers \u2013 thus reducing the likelihood yet further.<\/p>\n

\u201cEvaluations on the \u2018probabilistic\u2019 analysis looked at the flight time sequence, and the probability that TO will occur,\u201d notes from the meeting add. \u201c(We) looked at the probability of what event will be likely to occur that would required the crew to react, to a potential abort scenario they have to respond manually. In the final analysis, most of tasks can be\/will be done faster and more reliably by computer.\u201d<\/p>\n

See Also<\/h4>\n