Prevention of an Arms Race in Outer Space: Multilateral Negotiations’ Effects on International Law
Authors: Vestner T 
Published: November 2020

INTRODUCTION.Outerspaceis an increasingly competitive environment. This raises incentives for states to place conventional weapons in outer space. The 1967 Outer Space Treaty (OST), the applicable legal regime, is silent on the legality of the placement of conventional weapons, however. Since the early 1980’s, the multilateral diplomatic process on the Prevention of an Arms Race in Outer Space (PAROS) aims to explicitly prohibit the weaponization of outer space by a new international treaty. Yet states have not agreed on such a weapons ban treaty so far. This article analyses the multilateral negotiations’ effects on the applicable international law, namely the legal gap (lacuna) in the OST regime.MATERIALSANDMETHODS.Thisstudyanalyzestreatytexts,UNGeneralAssemblyresolutions,treatyproposals,states’workingpapers,states’statements,andreportsfrominternationalnegotiationsandmeetings. Th analytical framework is the rules for treaty interpretation according to the Vienna Convention on the Law of Treaties (VCLT). Consistent with explanatory and theory–building research, the methods used are those of historical legal research as well as general scientific methods, such as analysis, synthesis, analogy, description, and deduction.RESEARCHRESULTS.Thisarticleidentifis three mechanisms by which the multilateral negotiations on PAROS clarify and inform international law regarding the weaponization of outer space. First, the negotiationsledstatestocommunicatetheirlegalpositionsregardingtheissue.Thisclarifieshowstatesinterpretthelaw.ItalsoallowstoassesswhetherthecontinuousstatepracticetonotplacekineticweaponsinouterspacerepresentssubsequentpracticeoftheOSTaccordingtoArticle31(2)(b)VCLT.Second,thePAROSprocessproducedannualUNGeneralAssemblyresolutionsthatstrengthenedtheprincipleofpeacefuluseofouterspaceandlinkedit withstates’generalunderstandingthatthisimplieslimitstotheweaponizationofouterspace.Assuch,thisisrelevantfortheinterpretationofthegapinlightoftheOST’scontextandobjectandpurposeaccordingtoArticle31(1)VCLT.Third,thenegotiationshaveproducedpreciselanguageona prohibition of weaponization in the form of the draft Treaty on Prevention of the Placement of Weapons in Outer Space and of the Threat or Use of Force Against Outer Space Objects (PPWT), which enables the emergence of a prohibition under customary international law. For the interpretation of the OST’s gap, this would constitute “any relevant rules of international law” according to Article 31(3)(c) VCLT.DISCUSSIONANDCONCLUSIONS.Thisarticle arguesthatthemultilateralnegotiationshavebrokenthelegalsilenceregardingtheplacement ofconventionalweaponsinouterspace.Whilethethreemechanismshelptoidentifyandclarifythelaw,theyalsoinfluencethematerialsubstanceofthelaw.ThePA-ROSnegotiationshavenotledtheexistinglawtoclearlyprohibittheweaponizationofouterspace.Yetthenegotiationshaveinformedthelawsuchthattheexistinglawhardlyauthorizessuchaction.Theresultisthattheissueisunequivocallyregulatedbyinternationallaw,i.e.theOST’sgapisundoubtedlya legal gap. Yet the Lotus principle according to which what is not prohibited under international law is authorized falls short of the existing legal situation. This suggests that lex ferenda, the law in the making, has effects on lex lata. Multilateral negotiations – even deadlocked or failed ones – thus may be more than the making of future law but also the shaping of existing law. Accordingly, ongoing multilateral negotiations might be analyzed as supplementary means of treaty interpretation according to Article 32 VCLT. For policymakers, this suggests that negotiations may be used to influence the existing law, even if reaching agreement on a new treaty is not possible.