Editing CVEL

[[Image:Dualexpress.jpg|thumb|right|250px|Building a payload hierarchy with CVEL/GPDS]]
CVE-lite (abridged Common Vessel Extensions) is a programming library to aid developers of  add-on vessels for Orbiter. It extends the native Orbiter [[VESSEL]] class with additional functionality for multiple payloads, enhanced mesh handling or scenario-file based multistage support. It evolved from Dave Rowbotham's CVE library, cutting down on some of the internal complexity to allow for easier maintenance, and adding some new functionality.

CVEL implements the [[GPDS|Generic Payload Description System]] (GPDS) to allow the end user to express via simple lines in the scenario file any payload and, if using another CVEL vessel, any additional upper stages. Version-independent inter-vessel communication, as used by the library internally, is also extended to programmers by a companion library,  [[cvelmessage.dll]].

==History==
[[GPDS]] was conceived as a way to mount a payload of the end user's choice atop the [[Ariane 5]] as it was developed from a [[Multistage.dll|Vinka Multistage]] vessel to a standalone DLL.

It quickly became clear that combinations of payloads couldn't be specified. That is to say one couldn't mount an upper stage (eg. a [[Fregat]]) with a [[Probe]] on top of it. The two would necessarily have to jettison as separate vessels. This was not ideal and so an Inter-Vessel Payload Description interface was developed to allow communication between 'active' vessels (ie. to allow the Ariane 5 to tell the Fregat it should have a Probe attached).

The problem with this system (based on Rob Conley's COMMON_VESSEL class) was that, using C++ callbacks, calls between vessels compiled with different libraries would cause a crash. Something needed to be done.

Dave Rowbotham proposed extending the COMMON_VESSEL class to provide even more functionality. This included standardised mesh handling classes and an extensible GPDS handler. So was born [[CVE|COMMON_VESSEL_EX]] (CVE) which iterated through several beta variations building up an impressive array of supported vessels.

Unfortunately, CVE was also limited to interacting successfully only with other CVE vessels of the same library vintage, and the impressively complex library was slow to debug. [[CVEL|CVE-lite]] was an attempt to distill CVE into a lighter, more easily integratable system. Dropping some of the features of CVE for a closer release date and quicker debugging.

Crucially, CVEL also removed the need for vessels to all be compiled with the same library by introducing the messenger DLL ''cvelmessage.dll''. This enabled CVEL vessels to communicate not only with other CVEL vessels for the purposes of exchanging payload information, but to any other vessel about any information without requiring crash protection. Vessels that didn't support CVELmessage simply never receive the information.

Since the release of CVEL v1.0, there have been a large number of vessels released that support the system including, of course, the original Ariane 5 updated to version 2.

A beta library, including the Orbiter 2005 [[VESSEL2]] class updates was compiled and added to the downloads section of the [http://projectganymede.sourceforge.net/cve-lite/ CVEL website], and is considered by most to be stable for the current implementation of Orbiter.

==How to use GPDS2==

===The PAYLOAD tag===
Put simply GPDS allows users of CVE-lite compatible vessels to describe multiple payloads quickly and easily using the ''PAYLOAD'' tag in the scenario file.

<pre>PAYLOAD payloadname mesh class x y z mass xrot fuellevel</pre>

Here, "payloadname" is simply the alphanumeric name you wish the created payload to have.

"Mesh" is the name of the mesh file, including any paths off ~/Mesh that will represent the payload on the stack before it is separated, minus the ".msh"

"Class" is the payload's classname, such as "deltaglider" or "module1".

"x", "y" and "z" represent floating point offsets from the launching vessel's reference point (normally the centre of mass) that the mesh should be drawn. An example would be "0 0 4" for four metres along the centreline of the vessel.

"Mass" is the '''all-up-mass''' of the vessel that is to be created, '''INCLUDING''' fuel load. If you vary the loaded fuel (see later), you really ought to change this value here to be consistent.

"Xrot" is now sadly abandoned due to a limitation in Orbiter's current API, simply put a zero (0) here.

"Fuellevel" is the level (0->1) of fuel you wish the spawned payload to be equipped with. Not all vessels support the changing of their fuel state at creation, however. Most DLL-based craft won't unless they too are CVE-lite compatible, but most CFG-based vessels will quite happily. 

===The STAGE tag===
''STAGE''s are broadly similar to ''PAYLOAD'' *except* they constitute additional stages to your vessel. That is to say, if you mount a payload above a stage (and before and ''ENDSTAGE'' -- see below) it will separate WITH that "stage" vehicle and you may continue to loft the payload(s) before jettionning it later. An example would be the Soyuz launch vessel may configure a Fregat as a ''STAGE'' with the MarsExpress as a ''PAYLOAD'' above it.

<pre>STAGE payloadname mesh class x y z mass xrot fuellevel</pre>

(definitions as for PAYLOAD)

===The ENDSTAGE tag===

Differing to '''GPDS1''' and '''GPDS2''' here, the ''ENDSTAGE'' tag allows the user to close-off a substage and continue stacking payloads or more stages onto the launch vessel directly. It takes no parameters.

An example would be an Ariane 5 launching two fregats, both containing MarsExpress orbiters as ''PAYLOAD''s.


<pre>ENDSTAGE</pre>

==Examples==
Some basic (and not so basic!) examples.


===One Module-1 aboard a Proton-K from Baikonur.===
<pre>
Proton1:protonk
  STATUS Landed Earth
  BASE Baikonur:5
  HEADING 90.00
  FUEL 1.000
  CONFIGURATION 0
  PAYLOAD UserModule module1 module1 0 0 30 15000 0 1
END</pre>

Here the module1 mesh is loaded on the launcher 30 metres above its centre of mass. It weighs 15000. When it is jettisoned it will be of class "module1", fully fuelled (the 1 on the end) and be called "UserModule"

===Two Module-2s===

<pre>
  PAYLOAD UserModule1 module2 module2 0 0 27 8000 0 1
  PAYLOAD UserModule2 module2 module2 0 0 31 8000 0 1
</pre>

===Two Module-2s, each with their own CVE-lite fregat===


<pre>  STAGE Fregat1 fregat cvelfregat 0 0 27 7000 0 1
    PAYLOAD UserModule1 module2 module2 0 0 31 8000 0 1
  ENDSTAGE
  STAGE Fregat2 fregat cvelfregat 0 0 35 7000 0 1
    PAYLOAD UserModule2 module2 module2 0 0 39 8000 0 1
  ENDSTAGE</pre>



===MarsExpress probe on a fregat and star48 upper stages===

<pre>
  STAGE Fregat1 fregat cvelfregat 0 0 27 7000 0 1
    STAGE Star1 star48 star48 0 0 30 5000 0 1
      PAYLOAD MarsExpress mars_express_stowed mars_express_deployed 0 0 33 600 0 1
    ENDSTAGE
  ENDSTAGE</pre>



== CVEL-compatible vessels ==
=== Ariane 4 ===
[[Image:A4boost.png|thumb|right|Ariane 44LP blasting off from at Kourou]]

{{Addon|
1=[http://www.orbithangar.com/searchid.php?ID=674 Ariane 4 pack at orbithangar.com]|
2=David 'dh219' Henderson
}}

European [[Soyuz launchers|Soyuz-class]] booster. Now retired. See also from [[w:Ariane 4|Wikipedia]].

==== Recommended add-ons ==== 
[http://library.avsim.net/esearch.php?CatID=orbmisc&DLID=31333 Kourou Launch Centre]

=== Ariane 5 ===

[[Image:A5_logo1.jpg|thumb!right|Ariane 5 blasting off from the pad at Kourou]]

{{Addon|
1=[http://www.orbithangar.com/searchid.php?ID=583 Ariane 5 with ATV (CVEL) at orbithangar.com]|
2=David 'dh219' Henderson
}}

This [[add-on]] simulates three modern '''Ariane 5''' variants. The A5 G (Generic), the A5 ECA (enhanced with cryogenic second stage), and the hybrid A5 ATV (model that will be used to launch the European [[ATV]] ISS resupply craft). Using Thomas Ruth's beautiful free meshes and the [[CVEL|CVE-lite]] programming library, the Ariane 5 is the flagship of the [[CCCP Fleet|CCCP team's]] [[CVEL]] vessel fleet.

==Background==
Ariane 5 is a European heavy-lift launcher that operates out of [[Kourou]] in French Guiana. Capable of inserting up to 10 tonnes into a geostationary transfer orbit, or up to 21 tonnes into 51-degree LEO.

At liftoff, two solid rocket boosters (the EAPs) provide 90% of the thrust for 120 seconds before the central cryogenic stage (EPC), driven by a single French Vulcain or Vulcain-2 engine continues the ascent for approximately a further eight minutes.

The core lofts an upper stage fuelled either by a storable hypergolic propellent (the EPS) or another crogenic fuel (the ESC). restartable a number of times for complicated orbital insertions, including depositing the [[ATV]] into low-Earth orbit, multiple payload GTO insertions and interplanetary ejections or an enhanced for increased GTO payloads.

==The Simulation==
The simulation follows the published Ariane 5 specifications as closely as possible and includes the normal CCCP-fleet features of thrust vectoring, smoke where appropriate and full user-configurable flexibility over payloads thanks to the [[GPDS]] system provided by [[CVEL]].

Additional features include automatic engine throttling for max-Q, an optional automatic initial heading alignment program, non-restartable main stage and calculated centre of mass changes, including those produced by payloads.

==The ATV==
[[Image:Atv6.jpg|thumb|200px|right|ATV docked to ISS over Europe]]
As a bonus several other payload packages are included in the main download, these include Orbiterfan's [[Mars Express]], the Russian [[Fregat]] restartable upper stage, C3PO's orbital fuel tank, but probably most significantly, C3PO's [[ATV]].

The [[ATV]] is Europe's most visible contribution to the [[ISS]]. A 20-tonne Automated Transfer Vehicle intended to rendezvous and dock with the ISS to bring supplies, deorbit waste, provide reboost control and extend the living volume of the station by several cubic metres.

Despite following ESA and Arianespace's released information as closely as possible, many users have found it impossible to orbit the fully-loaded ATV with the default Ariane 5 ATV configuration in the pack, reducing the EPS's fuel load to 30% (PRPLEVEL 2:0.3) on launch seems to provide a more optimal setup.

The ATV has a fair amount of dV available to it, but its acceleration is pitiful. Plan ahead!

==== Recommended add-ons ==== 
[http://library.avsim.net/esearch.php?CatID=orbmisc&DLID=31333 Kourou Launch Centre]


=== Soyuz TMA ===
[[Image:Tmadg2.jpg|thumb|250px|right|Soyuz TMA docks to a DG4]]

{{Addon|
1=[http://www.orbithangar.com/searchid.php?ID=765 Soyuz TMA at orbithangar.com]|
2=David 'dh219' Henderson
}}

Using meshes from Jason 'Agent36' Benson and Jógvan 'C3PO' Trondesen, the '''Soyuz TMA''' has a realistic configuration, a particle-stream RCS system, animated panels and antennae and a ballistic reentry autopilot.

Launch on the [[Soyuz Launchers]] and perfect for use with the [[Progress]] and [[ATV]].

==See also==

[http://projectganymede.sourceforge.net/cve-lite/tutorials.html CVEL programming tutorial]

[[GPDS]]

==Links==
[[CCCP Fleet|The CCCP Fleet]]

[http://projectganymede.sourceforge.net/cve-lite/ The official CVEL homepage]

[http://sourceforge.net/project/showfiles.php?group_id=58685&package_id=124522 CCCP-Team CVE-Lite vessels]

[http://www.orbithangar.com/advsearch.cfm?search=name&text=CVE&S=Search CVE Search at Orbithangar]

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[[Category:Libraries]]