Editing Delta IV (section)

=== Proposed upgrades that were not implemented ===
Possible future upgrades for the Delta IV included adding extra strap-on solid motors, higher-thrust main engines, lighter materials, higher-thrust second stages, more (up to eight) strap-on CBCs, and a cryogenic propellant cross feed from strap on boosters to the common core.<ref name="Growth">{{Cite web |title=Delta Launch 310 – Delta IV Heavy Demo Media Kit - Delta Growth Options |url=http://www.boeing.com/defense-space/space/delta/kits/d310_d4heavy_demo.pdf |url-status=dead |archive-url=https://web.archive.org/web/20121006021346/http://www.boeing.com/defense-space/space/delta/kits/d310_d4heavy_demo.pdf |archive-date=October 6, 2012 |publisher=Boeing}}</ref>

At one point, NASA planned to use Delta IV or Atlas V to launch the proposed [[Orbital Space Plane Program|Orbital Space Plane]],<ref>{{Cite web |last=Whitesides |first=Loretta Hidalgo |date=July 9, 2008 |title=Why NASA Isn't Trying to Human-Rate the Atlas V or Delta IV Rockets |url=https://www.wired.com/wiredscience/2008/07/why-nasa-isnt-t/ |publisher=Wired |quote="You could launch a smaller human vehicle on a current expendable rocket [...] In fact, before the Columbia disaster NASA teams were working on an Orbital Space Plane (OSP) designed to do just that".}}</ref> which eventually became the [[Crew Exploration Vehicle]] and then the [[Orion (spacecraft)|Orion]]. Orion was intended to fly on the [[Ares I]] launch vehicle, then the [[Space Launch System]] after Ares I was cancelled.

In 2009, [[The Aerospace Corporation]] reported on [[NASA]] results of a study to determine the feasibility of modifying Delta IV to be [[Human-rating certification|crew-rated]] for use in NASA [[human spaceflight]] missions. According to [[Aviation Week & Space Technology]] the study, "found that a Delta IV heavy [...] could meet NASA's requirements for getting humans to low Earth orbit".<ref>{{Cite web |last=Frank Morring, Jr. |date=June 15, 2009 |title=Study Finds Human-rated Delta IV Cheaper |url=http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space&id=news/Study061509.xml |publisher=Aviation Week}}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

A proposed upgrade to the Delta IV family was the addition of extra solid motors. The Medium+ (4,4) would have used existing mount points to pair the four GEM 60s of the M+ (5,4) with the upper stage and fairing of the (4,2). An M+ (4,4) would have had a GTO payload of {{cvt|7500|kg}}, a LEO payload of {{cvt|14800|kg}}, and could have been available within 36 months of the first order. It was also considered to add extra GEM 60s to the M+ (5,4), which would have required adding extra attachment points, structural changes to cope with the different flight loads, and launch pad and infrastructure changes. The Medium+ (5,6) and (5,8) would have flown with six and eight SRBs respectively, for a maximum of up to {{cvt|9200|kg}} to GTO with the M+ (5,8). The Medium+ (5,6) and (5,8) could have been available within 48 months of the first order.<ref>{{Cite web |date=September 2007 |title=Delta IV Payload Planners Guide |url=http://www.ulalaunch.com/site/docs/product_cards/guides/DeltaIVPayloadPlannersGuide2007.pdf |archive-url=https://web.archive.org/web/20110722081616/http://www.ulalaunch.com/site/docs/product_cards/guides/DeltaIVPayloadPlannersGuide2007.pdf |archive-date=2011-07-22 |publisher=ULA |pages=10–15, 16}}</ref>