View source for Inertial Upper Stage

{{Short description|Space launch system}}
{{Infobox rocket stage
|image   =  Artist picture-Ulysses after deployment.jpg
|imsize  =  270
|caption =  Painting of [[Ulysses (spacecraft)|''Ulysses'']] deploying from the Space Shuttle
|name           =  Inertial Upper Stage
|manufacturer   =  [[Boeing]]<br/>[[United Technologies]]
|country-origin =  [[United States]]
|rockets     =  [[Space Shuttle]]<br/>[[Titan 34D]]<br/>[[Titan IV]]
|derivatives =  [[Transfer Orbit Stage|TOS]]
|height = {{convert|5.2|m|abbr=on}}<ref name="iusa">{{cite web|url=http://fas.org/spp/military/program/launch/ius.htm|title=Inertial Upper Stage|access-date=July 13, 2014|archive-date=March 11, 2016|archive-url=https://web.archive.org/web/20160311072224/http://fas.org/spp/military/program/launch/ius.htm|url-status=dead}}</ref>
|diameter = {{convert|2.8|m|abbr=on}}
|mass = {{convert|14,700|kg|abbr=on}}
|propmass = 
|status   =  Retired
|launches =  24
|success  =  21
|fail     =  2
|noburn   =  1
|first    =  30 October 1982
|last     =  14 February 2004<ref name="final">{{cite web |url=http://www.boeing.com/history/boeing/ius.html |title=Inertial Upper Stage |publisher=Boeing |access-date=21 July 2012 |archive-date=16 July 2012 |archive-url=https://web.archive.org/web/20120716204746/http://www.boeing.com/history/boeing/ius.html |url-status=dead }}</ref>
|stagedata    =  <!--insert one of the following templates for each stage:-->
  {{Infobox rocket/Stage
  |stageno    = First
  |type       = stage
  |length     = {{cvt|3.15|m}}<ref name="iusb">{{cite web|url=http://www.braeunig.us/space/specs/ius.htm|title=Inertial Upper Stage|access-date=21 July 2012}}</ref>
  |diameter   = {{cvt|2.34|m}}<ref name="iusb"/>
  |empty      =  
  |gross      =  {{convert|10,400|kg|abbr=on}}<ref name="iusb"/>
  |propmass   = {{convert|9,700|kg|abbr=on}}<ref name="iusa"/>
  |engines    = Orbus-21
  |thrust     = {{cvt|190|kN}}<ref name="iusa"/>
  |SI         = {{cvt|295.5|isp}}<ref name="iusb"/>
  |burntime   = up to 150 seconds<ref name="iusa"/>
  |fuel       = [[Solid fuel rocket|Solid]]
  }}
  {{Infobox rocket/Stage
  |stageno    = Second
  |type       = stage
  |length     = {{cvt|1.98|m}}<ref name="iusb"/>
  |diameter   = {{cvt|1.60|m}}<ref name="iusb"/>
  |empty      =  
  |gross      = {{cvt|3,000|kg}}
  |propmass   = {{cvt|2,700|kg}}<ref name="iusa"/>
  |engines    = Orbus-6
  |thrust     = {{cvt|80|kN}}<ref name="iusa"/>
  |SI         = {{cvt|289.1|isp}}<ref name="iusb"/>
  |burntime   =  
  |fuel       = [[Solid fuel rocket|Solid]]
  }}
}}

The '''Inertial Upper Stage''' ('''IUS'''), originally designated the '''Interim Upper Stage''', was a [[Multistage rocket|two-stage]], [[Solid-propellant rocket|solid-fueled]] space launch system developed by [[Boeing]] for the [[United States Air Force]] beginning in 1976<ref>{{cite news|title=Boeing launches two satellites|url=https://news.google.com/newspapers?nid=1243&dat=19821101&id=zJVTAAAAIBAJ&sjid=LYcDAAAAIBAJ&pg=5271,2172388|access-date=23 February 2014|newspaper=The Bulletin|date=1 November 1982|agency=UPI|pages=3|quote="Boeing won the contract to develop the IUS in 1976..."}}</ref> for raising payloads from [[low Earth orbit]] to higher orbits or interplanetary trajectories following launch aboard a [[Titan 34D]] or [[Titan IV]] rocket as its [[upper stage]], or from the payload bay of the [[Space Shuttle]] as a [[space tug]].

==Development==
During the development of the Space Shuttle, NASA, with support from the Air Force, wanted an upper stage that could be used on the Shuttle to deliver payloads from low earth orbit to higher energy orbits such as [[geostationary transfer orbit|GTO]] or [[geostationary orbit|GEO]] or to escape velocity for planetary probes. The candidates were the [[Centaur (rocket)|Centaur]], propelled by liquid hydrogen and liquid oxygen, the [[Transtage]], propelled by [[hypergolic]] storable propellants [[Aerozine-50]] and [[dinitrogen tetroxide]] ({{N2O4}}), and the Interim Upper Stage, using solid propellant. The [[US Department of Defense|DOD]] reported that Transtage could support all defense needs but could not meet NASA's scientific requirements, the IUS could support most defense needs and some science missions, while the Centaur could meet all needs of both the Air Force and NASA. Development began on both the Centaur and the IUS, and a second stage was added to the IUS design which could be used either as an [[apogee kick motor]] for inserting payloads directly into geostationary orbit or to increase the payload mass brought to escape velocity.<ref>{{cite web|author1=Virginia Dawson|author2=Mark Bowles|title=Taming liquid hydrogen : the Centaur upper stage rocket|url=https://history.nasa.gov/SP-4230.pdf|website=nasa.gov|access-date=July 24, 2014|page=172|quote=They argued that the IUS, which was designed by the Air Force, was a potentially better rocket. The first stage of the two-stage rocket was capable of launching medium-sized payloads at most. This limitation would be overcome by means of the addition of a second stage for larger payloads with destinations into deeper space. Specifically, the Air Force asked NASA to develop an additional stage that could be used for planetary missions such as a proposed probe to Jupiter called Galileo.}}</ref> 

[[Boeing]] was the primary contractor for the IUS<ref>{{cite web|url=https://www.globalsecurity.org/space/systems/t4-config-2b.htm|title=Titan IV Inertial Upper Stage (IUS)|website=www.globalsecurity.org|access-date=2 February 2019}}</ref> while Chemical Systems Division of [[United Technologies]] built the IUS solid rocket motors.<ref>{{cite web|url=http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/carriers.html|title=SPACE TRANSPORTATION SYSTEM PAYLOADS|website=science.ksc.nasa.gov|access-date=2 February 2019|archive-date=21 December 2016|archive-url=https://web.archive.org/web/20161221070222/http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/carriers.html|url-status=dead}}</ref>

When launched from the Space Shuttle, IUS could deliver up to {{Convert|2,270|kg|lb}} directly to GEO or up to {{Convert|4,940|kg|lb}} to [[Geosynchronous transfer orbit|GTO]].<ref name="iusb">{{cite web|url=http://www.braeunig.us/space/specs/ius.htm|title=Inertial Upper Stage|access-date=21 July 2012}}</ref>

The first launch of the IUS was in 1982 on a Titan 34D rocket from the [[Cape Canaveral Air Force Station]] shortly before the [[STS-6]] Space Shuttle mission.<ref>{{cite web|url=https://www.globalsecurity.org/space/library/report/1994/cape/cape2-6.htm|title=The Cape, Chapter 2, Section 6, TITAN 34D Military Space Operations and|website=www.globalsecurity.org|access-date=2 February 2019}}</ref> 

Development of the Shuttle-Centaur was halted after the [[Challenger disaster]], and the Interim Upper Stage became the Inertial Upper Stage.

==Design==
The solid rocket motor on both stages had a steerable nozzle for thrust vectoring. The second stage had [[hydrazine]] reaction control jets for attitude control whilst coasting, and for separation from payload.<ref name=STS-30-press-kit>{{cite web |url=https://science.ksc.nasa.gov/shuttle/missions/sts-30/sts-30-press-kit.txt |title=STS-30 PRESS KIT |date=April 1989 |quote=The IUS is 17 feet long and 9.25 ft. in diameter.  It consists of an aft skirt; an aft stage solid rocket motor (SRM) containing approximately 21,400 lb. of propellant and generating approximately 42,000 lb. of thrust; an interstage; a forward stage SRM with 6,000 lb. of propellant generating approximately  18,000 lb. of thrust; and an equipment support section. - The equipment support section contains the avionics, which provide guidance, navigation, control, telemetry, command and data management, reaction control and electrical power.  All mission-critical components of the avionics system, along with thrust vector actuators, reaction control thrusters, motor igniter and pyrotechnic stage separation equipment are redundant to assure better than 98 percent reliability. - The IUS two-stage vehicle uses both a large and small SRM.  These motors employ movable nozzles for thrust vector control.  The nozzles provide up to 4 degrees of steering on the large motor and 7 degrees on the small motor.  The large motor is the longest thrusting duration SRM ever developed for space, with the capability to thrust as long as 150 seconds.  Mission requirements and constraints (such as weight) can be met by tailoring the amount of propellant carried. |access-date=2020-07-25 |archive-date=2000-08-28 |archive-url=https://web.archive.org/web/20000828140155/https://science.ksc.nasa.gov/shuttle/missions/sts-30/sts-30-press-kit.txt |url-status=dead }}</ref> Depending on mission, one, two or three {{cvt|120|lb|kg|order=flip}} tanks of hydrazine could be fitted.<ref name=STS-30-press-kit/>

==Applications==
[[Image:Galileo Deployment (high res).jpg|left|thumb|250px|The ''Galileo'' spacecraft and its attached '''Inertial Upper Stage (IUS)''' booster being deployed after being launched by the [[Space Shuttle Atlantis|Space Shuttle ''Atlantis'']] on the [[STS-34]] mission]]
On Titan launches, the Titan booster would launch the IUS, carrying the payload into low Earth orbit where it was separated from the Titan and ignited its first stage, which carried it into an elliptical "transfer" orbit to a higher altitude. 

On Shuttle launches, the orbiter's payload bay was opened, the IUS and its payload raised (by the [[IUS Airborne Support Equipment]] (ASE)) to a 50-52° angle, and released.<ref name=STS-30-press-kit/> After the Shuttle separated from the payload to a safe distance, the IUS first stage ignited and, as on a Titan booster mission, entered a "transfer orbit". 

Upon reaching apogee in the transfer orbit, the first stage and interstage structure were jettisoned. The second stage then fired to circularize the orbit, after which it released the satellite and, using its attitude control jets, began a retrograde maneuver to enter a lower orbit to avoid any possibility of collision with its payload.

In addition to the communication and reconnaissance missions described above, which placed the payload into stationary (24-hour) orbit, the IUS was also used to boost spacecraft towards planetary trajectories. For these missions, the second IUS stage was separated and ignited immediately after first stage burnout. Igniting the second stage at low altitude (and thus, high orbital speed) provided the extra velocity the spacecraft needed to escape from Earth orbit (see [[Oberth effect]]). IUS could not impart as much velocity to its payload as Centaur would have been able to: while Centaur could have launched Galileo directly on a two-year trip to Jupiter, the IUS required a six-year voyage with multiple gravity assists.<ref>{{cite web|author1=Virginia Dawson|author2=Mark Bowles|title=Taming liquid hydrogen : the Centaur upper stage rocket|url=https://history.nasa.gov/SP-4230.pdf|website=nasa.gov|access-date=July 24, 2014|page=211}}</ref>

The final flight of the IUS occurred in February 2004.<ref name="final"/>

{{-}}

==Flights==
{{sticky header}}
{| class="wikitable sortable sticky-header"
|-
!Serial number<ref>{{cite web|url=http://space.skyrocket.de/doc_stage/ius.htm|title=IUS|first=Gunter|last=Krebs|work=Gunter's Space Page|access-date=21 July 2012}}</ref>
!Launch date
!Launch vehicle
!Payload
!Remarks
!Image
|-
|2
|1982-10-30
|[[Titan 34D]]
|{{nowrap|[[DSCS II F-16]]/[[DSCS III A-1|III A-1]]}}
|Mission successful despite telemetry loss for most of the flight.
|
|-
|1
|1983-04-04
|[[Space Shuttle]]<br/>{{OV|099|full=no}} ([[STS-6]])
|{{nowrap|[[TDRS-1|TDRS-A]] (TDRS-1)}}
|The second stage tumbled due to a thruster motor problem, resulting in an incorrect orbit. The Boeing staff that was monitoring the flight was able to separate the tumbling IUS from the satellite so it could be maneuvered into its final orbit. 
| [[File:STS-6 TDRS-A deploy preparations.jpg|60px]]
|-
|11
|1985-01-24
|[[Space Shuttle]]<br/>{{OV|103|full=no}} ([[STS-51-C]])
|[[USA-8]] ([[Magnum (satellite)|Magnum]])
|Classified DoD payload<ref name="magnum">{{cite web|last=Krebs|first=Gunter D.|title=Orion 1, 2 (Magnum 1, 2)|publisher=Gunter's Space Page.|access-date=December 5, 2022|url=https://space.skyrocket.de/doc_sdat/orion-1_nro.htm}}</ref>
|
|-
|12
|1985-10-03
|[[Space Shuttle]]<br/>{{OV|104|full=no}} ([[STS-51-J]])
|[[USA-11]]/[[USA-12|12]] ([[DSCS]])
|DoD payload. Declassified in 1998.<ref>{{Cite web |last=Mars |first=Kelli |date=2020-10-02 |title=35 Years Ago: STS-51J – First Flight of Space Shuttle Atlantis |url=http://www.nasa.gov/feature/35-years-ago-sts-51j-first-flight-of-space-shuttle-atlantis |access-date=2022-06-27 |website=NASA}}</ref>
|[[File:DSCS-III STS-51-J.jpg|frameless|78x78px]]
|-
|3
|1986-01-28
|[[Space Shuttle]]<br/>{{nowrap|{{OV|099|full=no}} ([[STS-51-L]])}}
|[[TDRS-B]]
|[[Space Shuttle Challenger disaster|Destroyed during launch]]<ref>{{cite web|url=https://www.spacecomm.nasa.gov/spacecomm/programs/tdrsS/default.cfm|archive-url=https://web.archive.org/web/20090320041300/https://www.spacecomm.nasa.gov/spacecomm/programs/tdrss/default.cfm|url-status=dead|archive-date=2009-03-20|title=Tracking and Data Relay Satellite System (TDRSS)|publisher=NASA Space Communications|access-date=2009-06-25}}</ref>
|
|-
|7
|1988-09-29
|[[Space Shuttle]]<br/>{{OV|103|full=no}} ([[STS-26]])
|[[TDRS-3|TDRS-C]] (TDRS-3)
|
| [[File:TDRS-C ASE.jpg|60px]]
|-
|9
|1989-03-13
|[[Space Shuttle]]<br/>{{OV|103|full=no}} ([[STS-29]])
|[[TDRS-4|TDRS-D]] (TDRS-4)
|
|
|-
|18
| 1989-05-04
| [[Space Shuttle]]<br/>{{OV|104|full=no}} ([[STS-30]])
| [[Magellan (spacecraft)|''Magellan'']]
| Probe to [[Venus]]. Only one tank of hydrazine.<ref name=STS-30-press-kit/>
| [[File:Magellan Overhead.jpg|60px]]
|-
|8
|1989-06-14
|[[Titan IV|Titan IV (402) A]]
|[[USA-39]] ([[Defense Support Program|DSP]])
|
|
|-
|19
|1989-10-18
|[[Space Shuttle]]<br/>{{OV|104|full=no}} ([[STS-34]])
|[[Galileo (spacecraft)|''Galileo'']]
| Probe to [[Jupiter]]
| [[File:STS034-71-000AK - STS-34 Galileo spacecraft IUS deployment sequence in OV-104's payload bay - 1989.jpg|60px]]
|-
|5
|1989-11-23
|[[Space Shuttle]]<br/>{{OV|103|full=no}} ([[STS-33]])
|[[USA-48]] ([[Magnum (satellite)|Magnum]])
|Classified DoD payload<ref name="magnum"/>
|
|-
|17
|1990-10-06
|[[Space Shuttle]]<br/>{{OV|103|full=no}} ([[STS-41]])
|[[Ulysses (spacecraft)|''Ulysses'']] on [[Payload Assist Module|PAM-S]]<!-- PAM-S must be included due to being a object deployed by IUS-->
| Probe to the polar regions of the [[Sun]]
| [[File:STS-41 Ulysses deployment.jpg|60px]]
|-
|6
|1990-11-13
|[[Titan IV|Titan IV (402) A]]
|[[USA-65]] ([[Defense Support Program|DSP]])
|
|
|-
|15
|1991-08-02
|[[Space Shuttle]]<br/>{{OV|104|full=no}} ([[STS-43]])
|[[TDRS-5|TDRS-E]] (TDRS-5)
|
| [[File:TDRS-E deployment from STS-43.jpg|60px]]
|-
|14
|1991-11-24
|[[Space Shuttle]]<br/>{{OV|104|full=no}} ([[STS-44]])
|[[USA-75]] ([[Defense Support Program|DSP]])
|
|
|-
|13
|1993-01-13
|[[Space Shuttle]]<br/>{{OV|105|full=no}} ([[STS-54]])
|[[TDRS-6|TDRS-F]] (TDRS-6)
|
| [[File:1993 s54 TDRS-F.jpg|60px]]
|-
|20
|1994-12-22
|[[Titan IV|Titan IV (402) A]]
|[[USA-107]] ([[Defense Support Program|DSP]])
|
|
|-
|26
|1995-07-13
|[[Space Shuttle]]<br/>{{OV|103|full=no}} ([[STS-70]])
|[[TDRS-7|TDRS-G]] (TDRS-7)
|
|
|-
|4
|1997-02-23
|[[Titan IV|Titan IV (402) B]]
|[[USA-130]] ([[Defense Support Program|DSP]])
|
|
|-
|21
|1999-04-09
|[[Titan IV|Titan IV (402) B]]
|[[USA-142]] ([[Defense Support Program|DSP]])
|IUS first and second stages failed to separate, payload placed into useless orbit
|
|-
|27
|1999-07-23
|[[Space Shuttle]]<br/>{{OV|102|full=no}} ([[STS-93]])
|[[Chandra X-ray Observatory]]
|Last launch of a payload using IUS on a Space Shuttle.
| [[File:Chandra X-ray Observatory inside the Space Shuttle payload bay.jpg|60px]]
|-
|22
|2000-05-08
|[[Titan IV|Titan IV (402) B]]
|[[USA-149]] ([[Defense Support Program|DSP]])
|
|
|-
|16
|2001-08-06
|[[Titan IV|Titan IV (402) B]]
|[[USA-159]] ([[Defense Support Program|DSP]])
|
|
|-
|10
|2004-02-14
|[[Titan IV|Titan IV (402) B]]
|[[USA-176]] ([[Defense Support Program|DSP]])
|
|
|-
|}

==Gallery==

<gallery>
File:1988 s26 TDRS-C.jpg|TDRS-C in Space Shuttle ''Discovery'''s payload bay
File:1988 s26TDRS-C Released.jpg|Release of TDRS-C
File:Ulysses sits atop the PAM-S and IUS combination.jpg|''Ulysses'' used a PAM-S and IUS combination
File:Inertial Upper Stage mockup.jpg|An Inertial Upper Stage at the [[Museum of Flight]] in Seattle 
</gallery>

== References ==
{{reflist}}

==External links==
* [https://web.archive.org/web/20140417071751/http://www.aerospace.org/wp-content/uploads/crosslink/V4N1.pdf ''Evolution of the Inertial Upper Stage''] ''Crosslink'' Winter 2003 Vol 4 Num 1 (published by The Aerospace Corporation), page 38
* [http://www.fas.org/spp/military/program/launch/ius.htm Inertial Upper Stage] at Federation of American Scientists

{{USAF space vehicles}}
{{Upper stages}}
{{Space Shuttle}}

[[Category:Expendable space launch systems]]
[[Category:Rocket stages]]
[[Category:Space Shuttle program]]